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Engineering 
Library 


GAS  ANALYSIS 


•s>— 

THE  MACMILLAN  COMPANY 

NEW  YORK   •   BOSTON   •   CHICAGO    •   DALLAS 
ATLANTA   •    SAN  FRANCISCO 

MACMILLAN  &  CO.,  LIMITED 

LONDON    •   BOMBAY    •  CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD. 

TORONTO 


GAS  ANALYSIS 


BY 
L.  M.  DENNIS 

M 

PROFESSOR    OF    INORGANIC    CHEMISTRY 
IN    CORNELL    UNIVERSITY 


THE   MACMILLAN   COMPANY 

1913 

Att  rights  reserved 


Engineering 
Library 


COPYRIGHT,  1902,  1913, 
BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.     Published  March,  1902.     Reprinted 
October,  1906;  June,  1910;  September,  1911;  September,  1912. 

New  edition,  April,  1913. 


/v. 


Koriaooti 

J.  8.  Cushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE 

In  general  plan  this  book  follows  the  last  edition  of  the  English 
translation  of  Hempel's  Methods  of  Gas  Analysis,  It  was  indeed 
begun  with  the  intention  of  having  it  serve  as  a  new  edition  of 
that  work,  but  the  many  advances  in  the  field  of  gas  analysis 
during  the  last  fourteen  years  have  necessitated  the  incorpora- 
tion of  much  new  material  and  the  modification  or  excision  of 
many  of  the  older  methods.  In  view  of  this  fact,  a  new  book  has 
been  written. 

With  the  kind  permission  of  Professor  Hempel,  full  descrip- 
tions of  his  classic  methods  for  both  technical  and  exact  gas 
analysis  have  been  incorporated  in  the  present  work,  although 
in  some  cases  the  apparatus  and  the  manner  of  its  manipulation 
have  been  modified. 

Procedures  for  the  determination  of  most  of  the  gases  that 
will  be  met  with  in  analytical  work  are  given  in  considerable 
detail.  Although  no  attempt  has  been  made  to  include  descrip- 
tions of  all  of  the  new  methods  that  have  recently  appeared, 
references  to  original  articles  are  given  throughout  the  work 
in  order  to  assist  the  reader  in  obtaining  more  complete  informa- 
tion upon  the  various  topics  than  could  be  included  in  a  labora- 
tory manual. 

The  separation  of  the  gases  of  the  argon  group  has  not  been 
discussed  for  the  reason  that  rapid  and  simple  analytical  methods 
for  the  determination  of  these  several  gases  have  not  as  yet  been 
perfected. 

Certain  methods  of  exact  analysis  that  are  adapted  to  specific 
determinations  have  been  described,  but  the  greater  part  of  the 
book  is  devoted  to  rapid  methods  of  technical  gas  analysis  be- 
cause it  is  in  this  division  of  the  field  that  most  of  the  work  of  the 
gas  analyst  will  lie. 


vi  PREFACE 

In  gas  analysis  the  accuracy  of  the  determination  is  probably 
dependent  to  a  greater  degree  upon  the  manipulatory  skill  with 
which  the  work  is  performed  than  in  any  other  branch  of  chemi- 
cal analysis.  It  is  for  this  reason  that  the  manipulation  of  each 
of  the  more  generally  used  types  of  apparatus  is  described  at 
length. 

I  desire  here  gratefully  to  acknowledge  the  assistance  that  has 
been  given  me  by  my  colleague  Dr.  R.  P.  Anderson  to  whom  I 
am  indebted  not  only  for  the  preparation  of  the  greater  portion 
of  the  chapter  dealing  with  the  combustion  of  gases,  but  also  for 
many  valuable  suggestions  and  for  a  careful  reading  of  the  proof- 
sheets.  I  take  pleasure  also  in  expressing  my  indebtedness  to 
Mr.  F.  H.  Rhodes  for  his  skillful  assistance  in  the  testing  of 
several  of  the  new  methods  of  analysis  that  are  here  described. 

L.  M.  DENNIS. 

ITHACA,  NEW  YORK, 
February,  1913. 


CONTENTS 

CHAPTER  I 

THE   COLLECTION  AND   STORAGE   OF   GASES 

PAGE 

Drawing  off  the  Sample I 

Sampling  Tubes 3 

Aspirators 7 

The  Mercury  Pump 8 

The  Topler  Pump 9 

Method  of  Working  the  Topler  Pump 12 

Collection  of  Gas  from  a  Mercury  Pump 13 

Collection  of  Gases  from  Springs. 15 

Collection  of  Gases  Dissolved  in  Liquids 16 

Collection  of  Gases  from  Reactions  in  Sealed  Tubes 21 

Extraction  of  Gases  from  Minerals 21 

Gasometers 23 

CHAPTER  II 

THE  MEASUREMENT  OF  LARGE  SAMPLES  OF  GAS 

Gas  Meter 28 

The  Rotameter 32 

CHAPTER  III 

THE  MEASUREMENT  OF  GASES 

The  Reduction  of  the  Volume  of  a  Gas  to  Standard  Conditions 33 

The  Law  of  Boyle 33 

The  Law  of  Charles 33 

The  Lunge  Gas  Volumeter 37 

The  Bodlander  Gas  Baroscope 40 


viii  CONTENTS 

CHAPTER  IV 

THE   DETERMINATION   OF   THE   SPECIFIC   GRAVITY  OF   A   GAS 

PAGE 

The  Determination  of  the  Specific  Gravity  of  a  Gas 

with  the  Apparatus  of  Bunsen •. 44 

with  the  Apparatus  of  Schilling 46 

with  the  apparatus  of  Pannertz 47 

CHAPTER  V 

ARRANGEMENT   AND   FITTINGS   OF   THE    LABORATORY 

Laboratory  for  Gas  Analysis 49 

CHAPTER  VI 

APPARATUS  FOR  GAS  ANALYSIS  WITH  WATER  AS  THE  CONFINING  LIQUID 

The  Hempel  Simple  Gas  Burette 51 

The  Hempel  Simple  Absorption  Pipettes 53 

The  Hempel  Simple  Absorption  Pipette  for  Liquid  Reagents.  ........  53 

The  Hempel  Simple  Absorption  Pipette  for  Solid  and  Liquid  Reagents  55 

The  Hempel  Double  Absorption  Pipettes 56 

The  Hempel  Double  Absorption  Pipette  for  Liquid  Reagents 56 

The  Hempel  Double  Absorption  Pipette  for  Solid  and  Liquid  Reagents  58 

Manipulation  of  the  Hempel  Apparatus 59 

Saturation  of  Confining  Water 59 

Filling  Burette  with  Confining  Liquid 59 

Measurement  of  100  cc 59 

Absorption  of  a  Gas 61 

Absorbing  Power  of  a  Reagent 65 

Accuracy  of  Analyses  with  the  Hempel  Apparatus 67 

Running  Down  of  Confining  Liquid 68 

Portable  Hempel  Apparatus 69 

The  Modified  Winkler  Gas  Burette 70 

Manipulation  of  the  Winkler  Burette 71 

The  Honigmann  Gas  Burette 72 

Manipulation  of  the  Honigmann  Burette 73 

The  Bunte  Gas  Burette 74 

Manipulation  of  the  Bunte  Burette 74 

The  Orsat-Dennis  Apparatus 78 

Manipulation  of  the  Orsat-Dennis  Apparatus 87 


CONTENTS  ix 
CHAPTER  VII 

THE  HEMPEL  APPARATUS  FOR  EXACT  GAS  ANALYSIS  WITH  MERCURY  AS  THE 

CONFINING   LIQUID 

PAGE 

Apparatus  with  Rubber  Connections  and  Glass  Stopcocks 90 

Gas  Burettes  with  Correction  for  Variations  in  Temperature  and  Bar- 
ometric Pressure 90 

The  Absorption  Pipettes 96 

The  Simple  Mercury  Absorption  Pipette 96 

The  Simple  Mercury  Absorption  Pipette  for  Solid  and  Liquid  Reagents  97 

The  Mercury  Absorption  Pipette  with  Absorption  Bulb 97 

Apparatus  for  Exact  Gas  Analysis  without  Rubber  Connections  or 

Stopcocks 99 

The  Measuring  Apparatus 101 

The  Measuring  Bulb 103 

Gas  Pipettes  for  Liquid  Absorbents 105 

Gas  Pipettes  for  Solid  Absorbents 107 

The  Absorption 109 

CHAPTER   VIII 

THE   CONSTRUCTION   AND   CONNECTION   OF   APPARATUS 

Glass  Blowing 113 

Mounting  of  Apparatus 114 

Rubber  Connections 114 

Lubrication  of  Stopcocks 115 

CHAPTER   IX 

PURIFICATION   OF    MERCURY 

Purification  of  Mercury  by  Nitric  Acid • 118 

Purification  of  Mercury  by  Concentrated  Sulphuric  Acid  and  Mercurous 

Sulphate 119 

Purification  of  Mercury  by  Distillation 119 

CHAPTER  X 

ABSORPTION  APPARATUS  FOR  USE  WITH  LARGE  VOLUMES  OF  GAS 

The  Friedrichs  Spiral  Gas  Washing  Bottle 123 

The  Winkler  Absorption  Apparatus .  124 


x  CONTENTS 

CHAPTER  XI 

THE   COMBUSTION   OF   GASES 

PAGE 

Possibilities  and  Limitations  of  the  Combustion  Method 127 

Gaseous  Hydrocarbons  and  Nitrogen 136 

Identification  of  Gaseous  Hydrocarbons 138 

CHAPTER  XII 

THE   DETERMINATION   OF   GASES   BY  COMBUSTION 

Analysis  by  Explosion 141 

The  Explosion  Pipette  for  Technical  Gas  Analysis 141 

Proportion  of  Gases  in  Analysis  by  Explosion : 143 

Formation  of  Oxides  of  Nitrogen 144 

Induction  Coil 144 

The  Hydrogen  Pipette 144 

Oxyhydrogen  Gas  Generator 145 

The  Explosion  Pipette  for  the  Hempel  Apparatus  for  Exact  Analysis. .  146 

Analysis  by  Combustion 147 

Combustion  with  an  Electrically  Heated  Platinum  Spiral 147 

The  Combustion  Pipette 147 

Manipulation  of  the  Combustion  Pipette 149 

Formation  of  Oxides  of  Nitrogen  in  Combustion  Pipette 152 

Combustion  with  a  Platinum  Capillary  Tube 154 

CHAPTER   XIII 

PROPERTIES  OF  THE  VARIOUS  GASES  AND  METHODS  FOR  THEIR  DETERMINATION 

Oxygen 158 

Properties  of  Oxygen 158 

Determination  of  Oxygen 158 

Determination  of  Oxygen  by  Combustion 159 

Determination  of  Oxygen  with  Copper  Eudiometer 159 

Determination  of  Oxygen  by  Absorption 160 

Alkaline  Pyrogallol 160 

Solid  Phosphorus 163 

Phosphorus  in  Solution 166 

Copper .' 166 

Solutions  of  Ferrous  Salts.  .  .168 


CONTENTS  xi 

PAGE 

Sodium  Hyposulphite 168 

Chromous  Chloride 169 

Ozone 170 

Properties  of  Ozone 170 

The  Detection  of  Ozone 170 

Examination  of  the  Gases  Produced  by  Burning  Hydrogen  in  Air  ....  175 
Examination  of  the  Gases  Produced  by  the  Silent  Electric  Discharge  in 

Air  and  Oxygen 1 76 

Examination  of  Gases  Produced  by  the  Action  of  Concentrated  Sul- 
phuric Acid  upon  Barium  Dioxide 177 

Examination  of  the  Gases  Produced  by  the  Slow  Oxidation  of  Phos- 
phorus in  Moist  Air 178 

Examination  of  the  Gases  Produced  by  the  Action  of  the  Flaming 

Electric  Arc  upon  Air 178 

Examination  of  Atmospheric  Air 178 

Determination  of  Ozone 179 

Hydrogen 181 

Properties  of  Hydrogen 181 

Detection  of  Hydrogen 181 

Determination  of  Hydrogen  by  Absorption 182 

Determination  of  Hydrogen  by  Explosion 186 

Determination  of  Hydrogen  with  Combustion  Pipette 187 

The  Absorption  of  Hydrogen  by  Palladium-black 188 

The  Fractional  Combustion  of  Hydrogen 191 

Fractional   Combustion   of   Hydrogen   with   Platinum   or   Palladium 

Asbestos 192 

Fractional  Combustion  of  Hydrogen  with  Palladium  Black 196 

Fractional  Combustion  of  Hydrogen  with  Copper  Oxide 198 

Nitrogen 206 

Properties  of  Nitrogen 206 

Absorption  of  Nitrogen 207 

Nitrous  Oxide _  .  .  213 

Properties  of  Nitrous  Oxide < ! 213 

Detection  of  Nitrous  Oxide 213 

Determination  of  Nitrous  Oxide 214 

Nitric  Oxide 217 

Properties  of  Nitric  Oxide 217 

Detection  of  Nitric  Oxide 218 

Determination  of  Nitric  Oxide 219 

Determination  of  Nitrites  in  the  Atmosphere 222 

Nitrogen  Tetroxide 223 

Properties  of  Nitrogen  Tetroxide 223 


xii  CONTENTS 

PAGE 

Ammonia 224 

Properties  of  Ammonia 224 

Detection  of  Ammonia 224 

Determination  of  Ammonia 224 

Carbon  Dioxide 225 

Properties  of  Carbon  Dioxide 225 

Determination  of  Carbon  Dioxide 225 

Carbon  Monoxide 226 

Properties  of  Carbon  Monoxide 226 

Detection  of  Carbon  Monoxide  by  Blood  Spectrum 226 

Detection  of  Carbon  Monoxide  by  means  of  Iodine  Pentoxide 231 

Determination  of  Carbon  Monoxide  by  Absorption 231 

Determination  of  Carbon  Monoxide  by  means  of  Iodine  Pentoxide  ...  235 

Colorimetric  Determination  of  Carbon  Monoxide 237 

Determination  of  Carbon  Monoxide  by  Fractional  Combustion 239 

Methane 240 

Properties  of  Methane 240 

Determination  of  Methane 241 

The  Heavy  Hydrocarbons 246 

Absorption  of  Heavy  Hydrocarbons 246 

Ethylene 248 

Properties  of  Ethylene 248 

Determination  of  Ethylene  by  Absorption 249 

Determination  of  Ethylene  in  presence  of  Acetylene 249 

Separation  of  Ethylene  from  Benzene 250 

Separation  of  Ethylene  from  Butylene. 250 

Propylene 250 

Acetylene 250 

Properties  of  Acetylene 250 

Determination  of  Acetylene 251 

Benzene 253 

Determination  of  Benzene 253 

Absorption  of  Benzene  by  Alcohol 253 

Absorption  of  Benzene  by  Paraffin  Oil • 254 

Determination  of  Benzene  as  Dinitrobenzene 254 

Separation  of  Benzene  from  Ethylene 255 

Absorption  of  Benzene  with  Nickel  Solution. 255 

Naphthalene 260 

Determination  of  Napthalene 260 

Cyanogen 262 

Properties  of  Cyanogen 262 

Detection  of  Cyanogen 262 


CONTENTS  xiii 

PAGE 

Determination  of  Cyanogen 263 

Detection  and  Determination  of  Cyanogen  in  presence  of  Hydrogen 

Cyanide 265 

Hydrogen  Cyanide 269 

Properties  of  Hydrogen  Cyanide 269 

Detection  of  Hydrogen  Cyanide 269 

Determination  of  Hydrogen  Cyanide 269 

Hydrogen  Sulphide 270 

Properties  of  Hydrogen  Sulphide 270 

Detection  of  Hydrogen  Sulphide 271 

Determination  of  Hydrogen  Sulphide 272 

Sulphur  Dioxide 273 

Properties  of  Sulphur  Dioxide 273 

Determination  of  Sulphur  Dioxide 274 

Determination  of  Sulphur  Dioxide  in  presence  of  Nitrous  Acid. 276 

Carbon  Oxysulphide 277 

Properties  of  Carbon  Oxysulphide 277 

Determination  of  Carbon  Oxysulphide 279 

Fluorine 280 

Determination  of  Fluorine 280 

Chlorine 284 

Properties  of  Chlorine 284 

Determination  of  Chlorine 285 

Hydrogen  Chloride 289 

Properties  of  Hydrogen  Chloride 289 

Determination  of  Hydrogen  Chloride 289 

Silicon  Tetrafluoride 290 

Phosphine 290 

Properties  of  Phosphine 290 

Determination  of  Phosphine 291 

Arsine 291 

Properties  of  Arsine 291 

Detection  of  Arsine * 293 

Determination  of  Arsine .• 293 

Stibine .* 293 

CHAPTER  XIV 

FLUE   GAS   ANALYSIS 

Sampling  of  Flue  Gas 296 

Analysis  of  Flue  Gas 297 

Automatic  Flue  Gas  Analysis 299 


xiv  CONTENTS 

PAGE 

The  Carbon  Dioxide  Recorder 299 

The  Autolysator 302 

The  Gas  Refractometer 304 


CHAPTER  XV 

ILLUMINATING   GAS  —  FUEL   GAS 

Coal   Gas  —  Pintsch    Gas  —  Water   Gas  —  Producer   Gas  —  Blast-Furnace 
Gas  —  Natural  Gas 

Coal  Gas 306 

The  Determination  of  the  Illuminating  Power  of  Coal  Gas 307 

The  Determination  of  the  Specific  Gravity  of  Coal  Gas .  ......  309 

The  Gas- Volumetric  Analysis  of  Coal  Gas 309 

The  Determination  of  the  Absorbable  Gases 310 

Carbon  Dioxide 311 

Benzene 312 

Other  Heavy  Hydrocarbons 312 

Oxygen 313 

Carbon  Monoxide 313 

Hydrogen,  Methane  (and  Ethane),  and  Nitrogen 314 

Nitrogen 317 

The  Determination  of  Naphthalene  in  Coal  Gas 318 

The  Determination  of  Total  Sulphur  in  Coal  Gas 319 

Determination  of  Sulphur  by  Drehschmidt-Hempel  Method 320 

Determination  of  Sulphur  by  Referees'  Method 324 

Young's  Volumetric  Method  for  Determination  of  Sulphur 327 

The  Determination  of  Cyanogen  in  Coal  Gas 328 

Pintsch  Gas 328 

Producer  Gas  —  Blast-Furnace  Gas 330 

CHAPTER  XVI 

THE  DETERMINATION  OF  THE  HEATING  VALUE  OF  FUEL 

The  Determination  of  the  Heating  Value  of  Solid  Fuels 331 

The  Bomb 331 

Preparation  of  Sample  of  Coal 333 

The  Calorimeter 335 

Preparation  of  the  Bomb 337 

Combustion  of  the  Sample , 339 


CONTENTS  xv 

PAGE 

The  Water  Equivalent  of  the  Calorimeter 340 

Standard  Combustible  Substances 341 

Example  of  the  Determination  of  the  Water  Equivalent  of  a  Calorimeter  342 

The  Radiation  Correction 343 

Example  of  the  Determination  of  the  Heating  Value  of  a  Sample  of  Coal  345 

The  Determination  of  the  Heating  Value  of  Liquid  and  Gaseous  Fuels  347 

The  Junkers  Gas  Calorimeter 347 

Preparation  of  Calorimeter 349 

Determination  of  the  Heating  Value  of  a  Gas 351 

Calculation  of  Results 352 

Gross  and  Net  Heating  Value 354 

Automatic  Gas  Calorimeter 354 

CHAPTER  XVII 

ACETYLENE   GAS 

Impurities  in  Commercial  Acetylene 355 

Sampling  of  Calcium  Carbide 356 

Determination  of  Hydrogen  in  Acetylene 356 

Determination  of  Ammonia  in  Acetylene 356 

Determination  of  Phosphine  in  Acetylene 357 

Determination  of  Volume  of  Acetylene  evolved  from  Sample  of  Carbide  363 

Calculation  of  Results 364 

Determination  of  Sulphur  in  Acetylene 367 

Determination  of  Silicon  Hydride  in  Acetylene 368 

Determination  of  Carbon  Monoxide  in  Acetylene 369 

Determination  of  Methane  in  Acetylene 369 

Determination  of  Oxygen  and  Nitrogen  in  Acetylene 369 

CHAPTER  XVIII 

EXAMINATION   OF   ATMOSPHERIC   AIR 

Composition  of  Atmospheric  Air 370 

Determination  of  Moisture  in  the  Atmosphere 371 

Absolute  and  Relative  Humidity 371 

Wet  and  Dry  Bulb  Thermometers 371 

The  Whirling  Psychrometer 372 

Manipulation  of  the  Whirling  Psychrometer 373 

Calculation  of  Results 374 

The  August  Psychrometer 375 

The  Hygrodeik 375 


xvi  CONTENTS 

PAGE 

Determination  of  Carbon  Dioxide  in  the  Atmosphere 376 

Methods  employed  in  Determination  of  Carbon  Dioxide  in  Air 377 

The  Hesse  Method 377 

Solutions  used  in  the  Hesse  Method 378 

Collection  of  Samples  of  Air 379 

Manipulation 379 

Calculation  of  Results 381 

The  Pettersson-Palmqvist  Method 382 

Anderson's  Modification  of  the  Pettersson-Palmqvist  Apparatus 387 


CHAPTER  XIX 

THE  ANALYSIS  OF  SALTPETER  AND  NITRIC  ACID  ESTERS  (NITROGLYCERINE, 
GUN-COTTON)  WITH  THE  NITROMETER 

The  Nitrometer 393 


CHAPTER  XX 

THE   LUNGE   NITROMETER 

The  Lunge  Nitrometer 397 

Manipulation  of  the  Lunge  Nitrometer 398 

The  Standardization  of  Potassium  Permanganate 400 

The  Determination  of  Active  Oxygen  in  Hydrogen  Dioxide 401 

The  Determination  of  the  Available  Chlorine  in  "Chloride  of  Lime".  .  401 

The  Evaluation  of  Pyrolusite 402 

The  Determination  of  Carbon  Dioxide  in  Sodium  Carbonate. 403 


International  Atomic  Weights,  1913 405 

Theoretical  Densities  of  Gases 406 

Reduction  of  a  Gas  Volume  to  o°  and  760  mm 407 

Tension  of  Aqueous  Vapor  from  —  2°  +  34° 411 


GAS  ANALYSIS 

CHAPTER  I 
THE  COLLECTION  AND  STORAGE  OF  GASES 

Drawing  off  the  Sample.  —  The  collection  of  a  sample  of  gas 
from  a  pipe,  conduit,  or  furnace  is  usually  accomplished  by 
inserting  into  the  chamber  a  tube  of  suitable  material  and 
drawing  off  the  gas  either  into  a  sampling  tube  or  bottle,  or 
directly  into  the  apparatus  in  which  the  gas  mixture  is  to  be 
analyzed.  If  the  gas  is  at  a  comparatively  low  temperature, 
it  may  be  drawn  off  through  a  tube  of  glass,  and  this  material 
or  porcelain  must  of  necessity  be  employed  if  the  gases  are  of  an 
acid  character.  At  temperatures  below  300°  a  small  lead  pipe 
will  be  found  convenient  because  of  its  flexibility.  At  higher 
temperatures  iron,  porcelain,  or  quartz  tubes  may  be  used.  If 
the  gases  are  very  hot,  the  tube  should  be  surrounded  by  a 
second  tube  through  which  cold  water  is  kept  circulating. 

A  satisfactory  form  of  such  a  tube  is  that  described  by  Wink- 
ler  in  1885. 1  It  consists  of  the  tubes  A,  and  C,  Fig.  i,  and  a 
third  tube,  lying  between  A  and  C,  to  which  the  side  arm  B 
is  attached.  The  tubes  are  made  of  metal,  either  copper  or 
iron  being  usually  employed.2  The  tube  A,  through  which  the 
gas  sample  is  drawn,  is  about  5  mm.  internal  diameter.  The 
tubes  are  kept  cool  by  running  water  which  enters  through  B, 
flows  through  C  and  escapes  through  the  outlet  D.  A  tube  of 
glass  or  lead  carrying  a  short  side  tube  is  attached  to  A,  and 

1  Lehrbuch  der  technischen  Gasanalyse,  ist  ed.,  p.  9. 

2  Frazer  and  Hoffman,  Bulletin  12,  Bureau  of  Mines,  suggest  the  use  of  an  inner 
tube  A  of  quartz. 

I 


2  GAS  ANALYSIS 


its  lurvtier  end  is'  connected  with  an  aspirator.  The  sample  of 
gas  to  be  analyzed  is  drawn  off  through  this  tube  into  the 
sampling  tube  or  gas  burette,  as  desired. 

Gas  mixtures  that  are  to  be  subjected  to  chemical  analysis 
should  never  be  passed  through  long  pieces  of  rubber  tubing. 
Rubber  is  not  only  porous,  but  it  may  also  absorb  certain  con- 
stituents of  the  gas  mixture.  These  absorbed  gases  or  even  the 
air  that  a  fresh  piece  of  rubber  tubing  contains  will  cling  tena- 
ciously to  the  walls  of  the  tube,  and  when  a  gas  mixture  of  other 
composition  is  passed  through  the  tube  they  will  slowly  but 
continuously  mix  with  the  entering  gas.  If  for  any  reason  the 
use  of  a  long  piece  of  rubber  tubing  cannot  be  avoided  in  the 
collection  or  transfer  of  a  sample  of  gas,  the  rubber  tube  should 
be  vigorously  rolled  between  the  palms  of  the  hands  while  the 


B 
FIG.  i 

sample  is  flowing  through  it,  in  order  to  detach  the  gas  adhering 
to  its  walls.  The  gas  that  passes  through  the  tube  during  this 
operation  should  of  course  be  discarded. 

When  short  pieces  of  rubber  tubing  are  used  for  connecting 
tubes  of  other  material,  the  ends  of  the  tubes  should  be  brought 
together  under  the  rubber  connector. 

A  sample  of  the  gaseous  products  of  combustion  from  a 
heating  apparatus  should  be  drawn  from  the  back  of  the  fire 
chamber:  further  up  in  the  flue  the  gas  will  usually  be  found  to 
contain  a  considerable  quantity  of  air  because  of  the  porosity 
of  the  wall. 

A  gas  mixture  flowing  through  a  pipe  is  frequently  of  varying 
composition  from  the  middle  of  the  pipe  toward  its  sides.  For 


THE   COLLECTION  AND   STORAGE  OF  GASES         3 

this  reason  the  sample  tube  that  is  inserted  into  the  gas  main 
should  extend  across  the  pipe  or  channel  from  side  to  side  and 
have  a  fine  longitudinal  slit  or  a  series  of  small  holes  through- 
out nearly  its  entire  length  in  the  main  so  that  the  sample  drawn 
off  will  show  as  nearly  as  possible  the  average  composition  of 
the  gas.1 

Sampling  Tubes.  —  If  the  place  where  the  gases  are  to  be 
collected  is  directly  accessible,  as,  for  example,  in  the  examina- 
tion of  mine  gases,  small  sampling  tubes  made  in  the  laboratory 
from  easily  fusible  glass  tubing  may  be  employed.  The  form 
used  by  Hempel  in  his  researches  "upon  the  composition  of  the 
atmosphere  at  different  parts  of  the  earth"  is  shown  in  Fig.  2. 
d  is  about  4  mm.  thick;  a,  6,  and  c,  only  i  mm.  These  tubes  were 
heated  in  an  air  bath  in  the  laboratory  to  200°,  and  were  then 


FIG.  2  FIG.  3 

exhausted  with  a  mercury  air-pump  and  fused  at  c.  By  simply 
breaking  the  tube  at  &,  it  fills  instantly  and  completely  with  the 
air  in  question.  The  tubes  are  then  closed  for  a  few  moments 
with  a  rubber  cap,  and  are  sealed  off  at  a  over  a  candle.  The 
exhausting  with  the  air-pump  has  the  advantage  of  rendering 
one  less  dependent  upon  the  care  of  the  person  who  fills  the  tubes. 
If,  however,  it  is  desired  to  avoid  this  exhausting,  the  tubes 
are  given  the  following  form  (Fig.  3).  To  fill  such  a  tube,  the  gas 
to  be  examined  is  drawn  through  it  and  the  tube  is  then  sealed  at 
a  and  b  by  fusion  in  a  candle  flame. 

Such  tubes  can  safely  be  shipped  by  packing  them  in  saw- 
dust in  boxes  that  have  a  separate  compartment  for  each  tube. 
The  boxes  themselves  are  placed  in  a  larger  box  filled  with  hay. 

A  somewhat  more  convenient  tube  for  collecting  gas  samples 
and  transporting  them  to  the  laboratory  for  analysis  is  that 

1  See  Metallurgical  and  Chemical  Engineering,  9  (1911),  303. 


4  GAS  ANALYSIS 

shown  in  Fig.  4.  The  tubes  used  in  the  Cornell  laboratory  vary 
from  16  cm.  x  3.5  cm.  (capacity  about  no  cc.)  to  25  cm.  x  4.5  cm., 
the  stopcocks  have  a  bore  one  mm.  in  diameter,  and  the  tube 
ends  beyond  the  stopcocks  are  capillary  tubes  of  six  mm.  ex- 
ternal diameter,  one  mm.  bore,  and  about  four  cm.  long.  If  the 
stopcocks  are  well  made  and  carefully  lubricated,  and  are  fast- 
ened securely  in  place  after  the  tube  is  filled  with  the  gas,  a 
sample  may  be  kept  for  a  considerable  length  of  time  in  such  a 
tube  without  undergoing  appreciable  change,  provided  the  gas 
mixture  does  not  act  upon  the  lubricant  of  the  stopcocks. 

In  equipping  a  laboratory  it  is  also  well  to  provide  some  of 
these  sampling  tubes  with  tailstoppers  (Fig.  5).     Such  stop- 


FIG.  4 

cocks  render  easy  the  elimination 
of  the  dead  space  in  the  end  capil- 
lary tubes  when  the  sample  is  trans- 
ferred to  the  gas  burette  (see  p.  59)  FlG-  5 
but  as  they  are  more  liable  to  leak  than  are  the  single  bore 
stopcocks,  tubes  that  are  fitted  with  them,  while  more  use- 
ful in  the  laboratory,  are  not  so  well  suited  to  the  transport  of 
gas  samples. 

These  tubes  are  filled  with  the  gas  sample  by  drawing  it 
through  the  tube  until  the  air  that  was  originally  in  the  tube 
is  entirely  displaced.  Naturally  this  presupposes  that  large 
amounts  of  gas  are  at  one's  disposal.  If  only  a  small  quantity  of 
gas  is  available,  the  tube  is  first  filled  with  water  or  mercury 
and  this  is  then  displaced  by  the  gas.  Water  can  be  used  only 
when  it  is  first  saturated  with  the  gas  mixture  that  is  being 
sampled  and  if  any  of  the  constituents  of  the  gas  mixture  are 


THE  COLLECTION  AND   STORAGE  OF   GASES 


H 


fairly  soluble  in  water,  as,  for  example,  ammonia  or  carbon 
dioxide,  mercury  must  be  employed  even  if  only  approximately 
accurate  results  are  desired. 

It  is  frequently  the  case  that  an  average  sample  of  the  gases 
passing  through  a  flue  or  pipe  during  a  period  of  several  hours  is 
desired.  Since  carbon  dioxide  is  always  present  in  flue  gases, 
mercury  must  be  used  as  the  confining  liquid  in  the  sample 
tube.  The  weight  and  costliness  of  mercury  make 
it  necessary  that  the  sample  tube  be  small,  and  this 
in  turn  renders  it  imperative  that  the  dead  space 
between  the  sample  tube  and  main  tube  be  elim- 
inated and  that  it  be  impossible  for  the  gas  in  B 
the  sampling  tube  to  diffuse  back  into  the  main 
tube  or  to  be  drawn  back  into  the  main  by  a  sud- 
den drop  in  the  pressure.  These  conditions  are 
fulfilled  by  the  clever  device  of  Huntly l  which  is 
shown  in  Fig.  6.  The  tube 2  is  first  filled  with  mer- 
cury up  to  the  top  of  the  bore  of  the  upper  stop- 
cock, and  both  stopcocks  are  closed.  The  capil- 
lary A  is  then  connected  with  the  branch  from 
the  main  tube,  and  the  stopcock  turned  so  that 
A  communicates  with  B.  The  air  in  A  is  thus 
driven  out  through  B.  If  the  pressure  in  the  main 
is  less  than  that  of  the  atmosphere,  suction  must 
be  applied  at  B.  The  upper  stopcock  is  then 
turned  through  180°  to  connect  A  with  C,  and  the 
lower  stopcock  is  carefully  opened  to  such  an 
extent  as  will  give  the  desired  speed  of  flow. 
Huntly  states  that  "it  has  been  found  by  trial  that  the  rate 
at  which  the  gas  is  drawn  in  is  constant  throughout  within  one 
per  cent." 

1  /.  Soc.  Chem.  Ind.,  29  (1910),  312. 

2  Huntly  does  not  give  the  dimensions  of  the  tube.    If  the  wide  part  of  the  tube 
were  about  18  cm.  long  and  3.5  cm.  diameter,  it  would  contain  quite  a  little  more 
than  100  cc.,  an  amount  sufficient  for  the  analysis. 


FIG.  6 


FIG.  7 


THE  COLLECTION  AND   STORAGE  OF  GASES         7 

If  the  tube  is  to  be  shipped  to  the  laboratory  after  the  sample 
has  been  taken,  some  mercury  should  be  left  in  the  capillary 
tube  above  the  stopcock  K,  and  the  tube  should  be  placed  in  a 
frame  that  will  support  it  in  an  upright  position.1 

Aspirators.  —  If  the  gases  to  be  collected  have  a  pressure  less 
than  the  prevailing  atmospheric  pressure,  an  aspirator  must  be 
employed  to  draw  them  over  into  the  sampling  apparatus.  The 
simplest  form  of  aspirator  consists  of  two  interchangeable  bottles 
of  equal  size  and  of  the  same  width  of  neck.  If  it  is  desired  to 
draw  off  a  sample  of  gas  for  analysis  while  the  mixture  is  being 
aspirated  the  arrangement  shown  in  Fig.  7  may  be  employed. 
The  water  flows  from  the  bottle  A  through  the  siphon  tube  G 
into  the  lower  bottle  C,  and  by  so  doing  draws  the  gas  through 
the  tube  F.  When  the  bottle  A  is  empty  C,  which  is  now  full, 
may  be  put  in  its  place  and  the  aspirating  of  the  gas  continued. 
The  gas  burette  is  connected  to  a  T-tube  in  the  manner  shown, 


FIG.  8 

is  filled  to  the  horizontal  tube  at  c  by  opening  the  pinchcocks 
d  and /and  raising  the  level-tube,  and  is  then  filled  with  a  sample 
by  lowering  the  level-tube  to  the  position  shown  in  the  figure. 
The  pinchcocks  d  and  /  are  then  closed  and  the  rubber  tube 
attached  to  the  burette  is  slipped  off  from'  the  small  glass  tube  e 
which  joins  the  two  short  pieces  of  rubber  tubing. 

Small  rubber  suction  bulbs,  Fig.  8,  may  at  times  be  found 
useful  for  drawing  a  gas  mixture  into  the  sampling  tube,  which 

1  In  Bulletin  No.  12  of  the  Bureau  of  Mines  (IQII)  Frazer  and  Hoffman  describe  a 
sampling  tube  that  is  patterned  after  that  of  Huntly,  but  is  inferior  to  the  latter  in 
that  it  does  not  carry  the  double  stopcocks  which  facilitate  the  elimination  of  the 
dead  space  in  the  capillary  tubes. 


8 


GAS  ANALYSIS 


should  be  placed  before  the  bulb  to  avoid  contact  of  the  rubber 
with  the  gas.  If  running  water  is  available,  a  water  suction 
pump  of  glass  (Fig.  9)  or  the  more  compact  and  durable  Chap- 
man pump  of  brass,  may  be  used  for  this  purpose. 

If  running  water  is  not  at  hand  a  suction 

pump  and  rubber  pressure  bulb  may  be  used 

for  drawing  the  gas 

through  the  appara- 
i      tus.     Fig.   10  shows 

such     an     arrange- 
ment,1   the    rubber 

pressure  bulb  being 

here     attached     to 

a   Finkener   suction 

pump.     The  rubber 

tube    on    the     side 

arm    of    the    pump 

is     joined     to     the 

apparatus     through 

which  the  gas  is  to 

be  drawn.    This  de- 
FIG.  9  vice   is    superior  to 

the  rubber  suction 
pump  in  that  stronger  suction  is 
obtained  and  the  bulb  does  not 
come  in  contact  with  the  gases 
which,  if  of  corrosive  nature,  would 
soon  destroy  it. 

With  such  an  apparatus  as  that  constructed  by  Korting,2 
steam  also  may  be  used  for  aspirating. 

The  Mercury  Pump.  —  A  mercury  pump  is  at  times  needed 
for  the  exhaustion  of  sample  tubes  like  those  described  on  p.  3, 
and  for  the  removal  and  collection  of  gases  in  certain  operations 

1  Ojferhaus,  J.f.  Gasbeleuchtung,  53  (1910),  806. 
2Gebr.  Korting  Akt.-Ges.,  Kortingsdorf  near  Hanover. 


FIG.  10 


THE   COLLECTION  AND   STORAGE  OF  GASES 


such  as  that  described  on  p.  22. 
Of  the  many  forms  of  mercury 
pumps  that  have  been  designed, 
that  of  Topler  is  one  of  the  most 
satisfactory.  The  construction  and 
operation  of  the  pump  have  been 
clearly  described  by  Travers,  from 
whose  book  on  the  "Experimental 
Study  of  Gases"  the  following  de- 
scription is  quoted: 

"  The  Topler  Pump.  —  The 
pump-chamber  A  (Fig.  n)  is 
made  of  stout  glass,  and  should  be 
about  200  mm.  long  and  50  mm. 
in  diameter;  the  ends,  and  partic- 
ularly the  upper  end,  should  be 
tapered  considerably  to  meet  tubes 
of  about  13  mm.  in  diameter.  If 
the  upper  end  of  the  pump- 
chamber  presents  a  surface  ap- 
proaching to  the  horizontal  to  the 
mercury  as  it  rises  to  the  pump- 
head,  films  or  even  bubbles  of  air 
may  be  entrapped  between  the 
mercury  and  the  glass,  and  ex- 
haustion will  be  slow.  The  side- 
tube  which  joins  the  vertical  tubes 
at  F  and  H  should  also  be  of 
about  13  mm.,  diameter;  the  in- 
ternal angle  between  the  two  tubes 
at  the  upper  junction  should,  for 
the  reasons  given  above,  be  very 
acute.  The  tube  C,  through  which 
the  gas  enters  the  pump,  should 
be  much  narrower  than  the  side- 


FIG.  ii 


io  GAS  ANALYSIS 

tube,  4  mm.  is  a  convenient  diameter;  if  it  is  not  made  so 
the  gas  which  enters  the  pump  while  the  mercury  is  still  fall- 
ing, may  carry  the  whole  of  the  mercury  in  the  side-tube  into 
the  upper  part  of  the  pump,  and  cause  a  serious  fracture.  If 
the  pump  is  properly  constructed,  the  gas  will  rise  in  bubbles 
between  the  mercury  and  the  glass. 

"The  vertical  tube  F  at  the  top  of  the  pump-chamber,  should 
be  tapered  to  meet  the  capillary  tube  (7,  which  should  be  bent 
on  itself  in  a  continuous  curve  of  about  3  cm.  in  diameter  imme- 
diately above  this  point.  The  length  of  the  capillary  tube  should 
be  about  800  mm.,  and  its  internal  diameter  should  not  much 
exceed  one  mm. ;  it  should  be  turned  up  at  its  lower  end  so  as  to 
admit  of  collecting  gases  through  the  pump.  The  capillary  tube 
may  easily  be  replaced  when  broken  if  a  sufficient  length  of  tube 
is  left  above  the  junction  at  F.  A  piece  of  tube,  of  the  same  diam- 
eter as  the  vertical  tube  of  the  pump,  is  first  sealed  to  a  straight 
piece  of  capillary  tube  of  sufficient  length.  The  tube  is  worked 
in  the  blowpipe  flame  till  a  perfectly  even  tapered  junction  is 
obtained;  it  is  then  bent,  cut  to  the  right  length,  and  sealed  to 
the  pump-head  with  the  aid  of  a  small  blowpipe.  The  efficiency 
of  the  pump  will  depend  to  a  great  extent  on  the  care  which  is 
expended  on  this  part  of  it. 

"The  lower  vertical  tube  should  be  so  long,  about  800  mm., 
that  when  there  is  a  vacuum  in  the  pump  and  the  mercury 
stands  below  the  level  of  the  joint  H,  the  lower  end  of  it  lies 
below  the  level  of  the  mercury  in  the  reservoir,  or  air  may  slowly 
leak  into  the  pump  through  the  junction  with  the  rubber  tube. 
The  rubber  tube  should  not  be  longer  than  is  necessary  to  allow 
of  the  reservoir  being  raised  to  the  level  of  the  pump-head, 
and  its  internal  diameter  should  be  nearly  as  large  as  that 
of  the  glass  tube  to  which  it  is  attached  so  as  to  allow  of  the 
free  flow  of  the  mercury.  In  order  to  obviate  any  chance  of  the 
rubber  tube  bursting,  it  should  be  sewn  into  a  strip  of  leather 
or  inclosed  in  a  piece  of  hollow  cotton  lamp- wick.1 

1  These  precautions  are  quite  unnecessary  if  enamelled  rubber  tubing  is  employed. 


THE   COLLECTION  AND   STORAGE  OF  GASES       n 

"In  order  to  prevent  the  mercury  from  passing  into  the  tube 
D,  containing  pentoxide  of  phosphorus,  when  the  reservoir  is 
raised,  the  tube  C  may  be  carried  vertically  upwards  to  a  height 
of  about  900  mm.  and  then  bent  on  itself.  It  is  more  convenient, 
however,  to  employ  a  glass  valve  V  as  in  the  figure,  and  it  is 
probable  that  the  rate  of  exhaustion  of  a  piece  of  apparatus 
attached  to  the  pump  would  be  considerably  decreased  by  the 
interposition  of  the  long  glass  tube.  The  valve  should  be  ground 
so  that  its  upper  surface  fits  sufficiently  accurately  into  the  inner 
surface  of  the  tube  containing  it  to  hinder  the  passage  of  the 
mercury;  the  angle  between  the  two  surfaces  should  be  very 
obtuse,  or  the  valve  may  tend  to  remain  closed  after  the  mercury 
has  fallen.  The  top  of  the  valve  should  be  on  a  level  with  the 
junction  F  (Fig.  n),  so  that  the  mercury  closes  it  before  it 
reaches  the  capillary  tube. 

"The  tube  D  containing  the  pentoxide  of  phosphorus1  is 
usually  connected  with  a  large  two-way  stopcock  T,  so  that  the 
pump  may  be  used  in  connection  with  more  than  one  piece  of 
apparatus. 

"The  pump  may  be  fixed  to  a  stout  board  as  in  the  figure. 
The  block  K  is  cut  so  that  the  bottom  of  the  pump-chamber 
rests  on  it,  and  is  kept  in  place  by  means  of  a  strip  of  brass 
and  a  couple  of  screws. 

"  The  fall-tube  passes  through  a  hole  in  the  bottom  of  the 
tray;  a  cork  fitting  closely  to  the  fall- tube  serves  to  keep  it 
firmly  in  place,  and  to  prevent  the  escape  of  mercury  through 
the  hole.  The  tray  supports  the  basin  into  which  the  end  of 
the  capillary  tube  dips.  The  board  to  which  the  pump  is 

1  This  reagent  is  almost  universally  used  as  a  dehydrating  reagent  in  working 
with  gases,  but  it  is  somewhat  difficult  to  obtain  pure.  The  oxide  should  be  per- 
fectly white  and  quite  free  from  discolored  nodules  and  sticky  masses  of  meta- 
phosphoric  acid.  When  exposed  to  the  air  it  should  deliquesce  without  turning  red 
or  giving  off  any  odor.  The  principal  impurities  consist  of  the  lower  oxides  of 
phosphorus,  some  of  which  are  in  themselves  volatile  and  react  with  gases,  such  as 
chlorine  and  ozone,  and  with  water  vapor  to  yield  phosphoretted  hydrogen.  The 
pentoxide  can  be  obtained  absolutely  free  from  the  lower  oxides  by  throwing  it  into 
a  red-hot  porcelain  basin,  and  stirring  it  in  a  current  of  oxygen. 


12  GAS  ANALYSIS 

attached  may  be  screwed  to  the  wall  at  a  convenient  height, 
or  fixed  to  a  stand. 

"  The  reservoir  may  be  placed  in  a  bracket,  or  supported  in  a 
retort  ring  with  a  piece  cut  out  of  it  to  allow  of  the  passage  of  the 
rubber  tube.  The  retort  ring  may  be  fixed  to  an  iron  rod  passing 
through  holes  in  the  tray  and  stand.  A  pulley  and  cord  may  be 
found  convenient  in  working  large  pumps. 

"  Method  of  Working  the  Topler  Pump. —  The  pump  is  first 
carefully  cleaned  with  chromic  and  sulphuric  acids,  washed  with 
distilled  water  and  alcohol  and  dried.  It  is  then  set  up  on  the 
stand,  the  tube  C  is  sealed  to  the  tube  D,  containing  pentoxide 
of  phosphorus,  and  the  rubber  tube  and  reservoir  B  are  attached. 
When  sufficient  mercury  has  been  poured  into  the  reservoir  and 
trough  the  pump  is  ready  for  use. 

"The  reservoir  is  raised  so  as  to  expel  about  two-thirds  of  the 
air  in  the  pump-chamber  through  the  capillary  tube,  and  is 
then  lowered.  As  the  mercury  falls  the  air  in  the  tube  containing 
the  pentoxide  forces  its  way  through  the  mercury  in  the  side 
tube,  and  enters  the  pump.  The  operation  is  then  repeated,  but 
during  the  first  few  strokes  the  air  should  not  be  completely 
expelled  from  the  pump-chamber.  If  this  precaution  is  not 
taken  the  air  will  begin  to  enter  the  side-tube,  while  it  still 
contains  a  long  column  of  mercury;  it  will  not  then  break  up 
into  bubbles,  but  will  probably  carry  the  whole  of  the  mercury 
upwards  against  the  junction  F  causing  a  serious  fracture.  On 
no  account  should  the  tap  T  be  opened  while  the  mercury  is 
falling  in  the  pump-chamber,  or  a  similar  accident  may  result. 
In  any  case  the  gas  should  only  be  allowed  to  enter  the  pump 
slowly.  A  rapid  current  of  gas  may  impact  the  pentoxide 
of  phosphorus  into  the  end  of  the  tube  containing  it,  and  render 
subsequent  exhaustion  very  slow. 

"  During  the  last  stages  of  the  process  of  exhaustion  care  must 
be  taken  that  the  mercury  does  not  come  into  violent  contact 
with  the  top  of  the  pump,  or  a  fracture  may  result.  The  mer- 
cury may  be  allowed  to  rise  rapidly  to  the  junction  F;  it  may  then 


THE   COLLECTION  AND   STORAGE   OF   GASES 


R 


be  checked  either  by  pinching  the  rubber  tube  or  by  lowering  the 
reservoir.    With  practice  the  action  becomes  automatic. 

"When  a  pump  is  first  set  up  it  should  be  allowed  to  remain 
exhausted  for  a  sufficient  time 
for  the  complete  absorption  of 
water  in  the  apparatus  by  the 
pentoxide  of  phosphorus.  Fur- 
ther, since  gases  like  carbon 
dioxide  condense  in  considerable 
quantity  on  glass  surfaces,  the 
maximum  efficiency  will  not  be 
reached  till  the  pump  has  been 
filled  with  air,  and  exhausted 
two  or  three  times." 

Collection  of  Gas  from  the 
Mercury  Pump.  —  The  method 
described  by  Travers  for  collect- 
ing the  gases  that  are  drawn  by 
the  pump  from  a  container  con- 
sists in  filling  a  tube  with  mer- 
cury and  inverting  this  over  the 
end  of  the  capillary  tube  G. 
According  to  Keyes  l  this  pro- 
cedure is  open  to  objection  be- 
cause there  is  always  present 
between  the  mercury  and  the 
walls  of  the  connecting  tube,  a 
film  of  air  that  cannot,  in  the 
Travers'  method  of  manipula- 
tion, be  removed  from  the  tube 
before  the  gas  sample  is  driven 
into  it.  To  remedy  this  diffi- 
culty Keyes  fuses  the  sampling  tube  S,  Fig.  12,  to  the  upturned 
end  of  the  capillary  tube  G,  Fig.  n.  A  small  trap  /  is  fused  to 

1  /.  Am.  Chem.  Soe.,  31  (1909),  1271. 


FiG.   12 


14  GAS  ANALYSIS 

the  lower  end  of  5  and  this  is  connected  to  the  level-bulb  M . 
At  the  upper  end  of  ,5"  is  a  double-bore  stopcock  N.  If  the  mer- 
cury pump  is  to  be  used  simply  to  exhaust  a  container,  stop- 
cock N  is  left  open  to  the  air  with  the  mercury  standing  at  the 
level  shown  in  the  figure  during  the  first  few  strokes.  When  the 
exhaustion  of  the  apparatus  is  nearly  complete,  the  level  bulb  M 
may  be  raised  to  expel  the  air  from  the  tube  S.  The  stopcock  N 
is  then  closed  and  upon  lowering  the  level  bulb  a  fair  vacuum 
will  result  in  S  which  will  facilitate  the  escape  into  this  tube 
of  the  bubbles  of  gas  passing  downward  through  the  capillary 
tube  of  the  pump. 

To  collect  the  gas  that  is  discharged  from  the  pump  the  tube 
5  is  connected  to  a  gas  burette  R  by  a  bent  capillary  tube  and 
short  connectors  of  rubber  tubing  in  the  manner  shown  in  the 
figure.  Mercury  is  used  as  the  confining  liquid  in  R  as  well  as 
in  S.  The  level  tube  of  the  burette  R  is  raised  and  the  air  in 
the  burette  is  driven  over  into  the  collecting  tube  ,5.  The  stop- 
cock W  of  the  burette  is  then  closed  and  the  air  adhering  to  the 
walls  of  the  burette  is  caused  to  collect  at  the  top  of  the  tube  by 
lowering  the  level  tube  of  the  burette  and  thus  bringing  the 
tube  under  diminished  pressure.  The  air  thus  released  is  ex- 
pelled from  the  burette  by  raising  the  level  tube  and  opening 
the  stopcock  W.  The  air  in  the  collecting  tube  6*  is  driven  out 
by  first  raising  the  level  bulb  M  and  driving  out  most  of  the  air 
in  the  tube  through  the  bore  of  the  stopcock  N  that  communi- 
cates with  the  open  air.  N  is  then  closed,  the  level  bulb  is 
lowered,  and  the  air  thus  liberated  from  the  walls  of  the  tube  5 
is  driven  out  through  the  stopcock  by  raising  M.  Upon  re- 
peating these  operations  several  times  the  collecting  tube  and 
the  gas  burette  may  be  rendered  practically  free  from  gas  (air). 
The  mercury  pump  is  now  started  and  the  gas  to  be  collected 
is  driven  over  directly  into  the  tube  S.  At  the  conclusion  of  the 
pumping  this  gas  is  passed  over  into  the  burette  R  by  raising 
the  level  bulb  M  and  turning  the  two  stopcocks  to  the  proper 
positions.  Any  minute  gas  bubbles  that  may  have  lodged 


THE  COLLECTION  AND   STORAGE  OF  GASES       15 


between  the  mercury  and  the  glass  walls  can  easily  be  set  free 
and  recovered  by  the  manipulation  above  described. 

Collection  of  Gases  from  Springs.  —  To  collect  gas  from 
springs  that  are  directly  accessible,  the  small  apparatus  pro- 
posed by  Bunsen  1  may  be  used  (Fig.  13). 

This  consists  of  a  test-tube  c  of  from 
40  to  60  cc.  capacity,  drawn  out  at  a  be- 
fore the  blast-lamp  to  the  size  of  a  fine 
straw,  and  connected  air-tight  with  the 
funnel  b  by  means  of  a  well-fitting  cork 
or  a  piece  of  rubber  tubing.  The  ap- 
paratus is  then  filled  with  the  water  of 
the  spring.  This  cannot  be  done  without 
access  of  air,  which  would  change  the 
composition  of  the  gases  dissolved  in  the 
spring  water  in  the  tube.  Hence  the  in- 
verted apparatus,  with  the  mouth  of  the 
funnel  upward,  is  lowered  below  the  level 
of  the  spring,  and,  with  a  narrow  tube 
reaching  to  the  bottom  of  the  test-tube, 
the  water  that  in  the  first  filling  had 
come  in  contact  with  the  air  is  sucked  out 


FIG.  13 


until  one  is  satisfied  that  it  has  been  entirely  replaced  by  other 
water  from  the  spring.  If  now  the  gas  of  the  spring  is  allowed  to 
rise  through  the  funnel  into  the  test-tube  thus  filled,  the  purity 
of  the  sample  is  assured.  If  the  rising  bubbles  stop  in  the  neck 
of  the  funnel  or  at  the  contraction  a,  they  can  easily  be  made  to 
ascend  by  tapping  the  edge  of  the  funnel  upon  some  hard  sub- 
stance. The  apparatus  is  then  placed  in  a  small  dish  and  re- 
moved from  the  spring,  and  the  tube  is  sealed  by  fusion  at  a. 
This  can  easily  be  done  with  the  blow-pipe,  the  moisture  at  the 
point  a  having  first  been  driven  away  by  warming. 
W.  Ramsay  and  M.  W.  Travers2  have  proposed  the  apparatus 

1  Bunsen,  Gasometrische  Methoden,  2d  ed.,  p.  2. 

2  Proc.  Royal  Soc.,  London,  60  (1896).  442. 


i6 


GAS  ANALYSIS 


shown  in  Fig.  14  for  collecting  large  quantities  of  gases  from 
mineral  waters.  The  cylinder  A  is  filled  with  the  water  of 
the  spring,  and  the  rising  bubbles  of  gas  pass  into  the  cylinder 
through  the  funnel  D  and  the  tube  C. 

Collection  of  Gases  dis- 
solved in  Liquids.  —  For  the 
determination  of  the  volume  and 
composition  of  the  dissolved 
gases  in  liquids,  the  Tiemann 
and  Preusse  modification  of 
Reichardt's  apparatus  1  can  be 
recommended  (Fig.  15). 

This  consists  of  two  flasks  A 
and  B,  each  of  about  i  liter 
capacity,  and  connected  by 
tubes  with  the  gas-collector  C. 
The  flask  A  is  fitted  with  a  per- 
forated rubber  stopper  in  which 
is  inserted  the  glass  tube  a  bent 
at  a  right  angle  and  ending  flush 
with  the  lower  surface  of  the 
stopper,  a  is  joined  by  a  piece 
of  rubber  tubing  to  the  tube  be, 
jjl  which  in  turn  connects  with  the 
gas-collector  C.  C  is  held  by 
a  clamp,  has  a  diameter  of  35 
mm.,  is  about  300  mm.  long, 
and  at  the  upper  end  is  drawn 
out  to  a  short,  narrow,  and 


FIG.  14 


narrow, 

slightly  bent  tube  that  can  be  closed  with  the  rubber  tube  and 
pinchcock  g.  In  the  lower  end  of  C  is  a  rubber  stopper  with 
two  holes  through  one  of  which  the  tube  be,  projecting  about 
80  mm.  into  C,  is  inserted.  Though  the  other  opening  passes 
the  tube  d  which  extends  only  slightly  beyond  the  stopper 

1  Berichte  der  deutschen  chemischen  Gesellschaft,  12  (1879),  1768. 


THE   COLLECTION  AND   STORAGE  OF   GASES       17 

and  connects  C  with  the  flask  B.  B  has  a  double-bore  rubber 
stopper  carrying  the  tubes  e  and  /.  e  ends  about  10  mm. 
above  the  bottom  of  the  flask,  and  above  the  stopper  it  is 
bent  at  a  right  angle  and  is  connected  with  d.  The  tube  /, 
which  need  not  project  below  the  stopper,  carries  a  thin  rubber 
tube  x  about  i  m.  in  length  and  provided  with  a  mouthpiece. 
A  pinchcock  for  closing  the  rubber  tube  between  a  and  b  is  also 
needed. 


FIG.  15 

The  apparatus  thus  arranged  is  made  ready  for  a  determina- 
tion by  filling  the  flask  B  somewhat  more  than  half  full  of  boiled 
water  and  removing  the  flask  A  by  slipping  the  tube  a  out  of  the 
rubber  connection;  then,  by  blowing  into  the  rubber  tube  x, 
water  is  driven  over  from  the  flask  B  into  the  gas-collector 
C  and  the  adjoining  tubes,  until  the  air  is  wholly  displaced. 
The  rubber  tubes  at  b  and  g  are  now  closed  with  pinchcocks. 
The  flask  A  is  then  filled  to  the  brim  with  distilled  water,  the 
stopper  is  inserted,  water  being  thereby  driven  into  the  tube  a, 
and  the  flask  is  again  connected  with  b,  the  pinchcock  being 
opened. 


1 8  GAS  ANALYSIS 

The  water  in  B  is  now  heated  to  gentle  boiling,  and  that  in  A 
is  allowed  to  boil  somewhat  more  rapidly.  The  absorbed  air 
is  thus  driven  out,  and  the  gases  which  are  dissolved  in  the  water 
in  A  and  C  collect  in  the  upper  part  of  C,  from  which  they  are 
removed  by  occasionally  opening  the  pinchcock  at  g  and  blowing 
into  the  rubber  tube  x. 

When,  upon  cooling  the  apparatus,  the  gases  that  have  col- 
lected disappear,  the  heating  of  the  flask  A  is  discontinued,  the 
pinchcock  between  a  and  b  is  closed,  and  A  is  disconnected  and 
emptied.  The  water  in  C  and  B  is  now  entirely  free  from  ab- 
sorbed gases,  and  air  cannot  enter  from  without  because  the 
liquid  in  B  is  kept  continually  boiling.  The  apparatus  is  now 
ready  for  a  determination,  which  is  made  as  follows:  — 

The  cooled  flask  A,  whose  capacity  has  previously  been 
determined,  is  filled  with  the  water  to  be  examined,  and  the 
stopper  is  pressed  in  so  far  that  the  air  in  the  tube  a  is  completely 
driven  out.  a  is  then  connected  with  b,  care  being  taken  that 
in  so  doing  no  air-bubbles  are  inclosed.  The  pinchcock  between 
a  and  b  is  opened,  and  the  water  in  A  is  heated  to  gentle  boiling. 
The  dissolved  gases  are  hereby  driven  over  into  the  gas-collector 
C.  Steam  is  formed  at  the  same  time.  The  heating  of  the  flask 
A  must  now  be  so  regulated  that  the  gas  and  steam  evolved 
never  drive  out  more  than  half  the  liquid  in  C:  otherwise  there 
is  danger  of  gas-bubbles  entering  the  tubes  d  and  e  and  thus 
escaping. 

After  heating  for  about  twenty  minutes,  the  flame  under  A 
is  removed.  In  a  few  minutes  the  steam  in  A  and  C  condenses, 
and  water  passes  from  B  toward  C  and  A.  If  a  gas-bubble 
is  observed  in  A ,  the  flask  A  must  again  be  heated  and  cooled  in 
the  manner  just  described.  The  operation  is  ended  when  the  hot 
liquid  flows  back  and  completely  fills  A.  The  rubber  tube  g 
is  then  connected  with  a  small  tube  which  is  filled  with  water 
or  mercury,  and  the  gas  standing  over  the  hot  liquid  in  C  is 
driven  over  into  a  eudiometer,  gas  burette,  or  gasometer  by 
blowing  into  the  tube  x  and  opening  the  pinchcock  g. 


THE   COLLECTION  AND   STORAGE  OF  GASES       19 

F.  Hoppe-Seyler  1  has  devised  a  somewhat  more  complicated 
apparatus  for  extracting  the  dissolved  gases  from  the  waters  of 
springs  and  rivers.  It  is  a  modification  of  the  method  proposed 
by  Bunsen  and  Dittmar.  The  apparatus  shown  in  Fig.  16 
varies  slightly  from  that  suggested  by  Hoppe-Seyler  in  that  a 
gas  burette  D  (see  page  91)  is  used  as  the  collecting  vessel  and 
air-pump.  Any  other  burette  with  a  two-way  stopcock  may, 


FIG.  16 

of  course,  be  employed  in  place  of  the  burette  here  figured.  The 
apparatus  consists  of  the  gas  burette  D  filled  with  mercury, 
the  glass  tubes,  A,  B,  and  C,  and  the  level-bulb  F.  The  tubes 
A,  B,  and  C  are  joined  together  with  pieces  of  rubber  tubing. 
Screw  pinchcocks  are  placed  at  a  and  b.  To  extract  the  dissolved 
gases  from  a  sample  of  water,  a  bent  glass  tube  is  inserted  at  b 
and  the  tubes  A  and  C  are  filled  with  mercury  by  raising  the 

1  Zeitschr.f.  analyt.  Chem.,  31  (1892),  367. 


20  GAS  ANALYSIS 

level-bulb  F,  the  mercury  being  allowed  to  rise  until  it  reaches 
the  tube  which  has  been  inserted  at  b.  The  glass  tube  is  then 
introduced  into  the  vessel  that  contains  the  water  to  be  ex- 
amined, and  by  lowering  the  level-bulb  F  water  is  drawn  into 
the  apparatus  until  the  tube  A  is  completely  filled  with  it.  The 
bent  tube  is  then  removed  from  b,  B  is  inserted  in  its  place,  and 
the  pinchcock  at  b  is  closed.  The  two-way  stopcock  of  the 
burette  is  now  turned  so  that  the  burette  communicates  with 
the  exit  tube  /.  The  air  in  the  burette  is  driven  out  by  raising 
the  level-bulb  E,  and  the  stopcock  g  is  then  turned  so  that  the 
burette  communicates  with  the  tube  B.  Upon  lowering  the 
level-bulb  as  far  as  possible  the  burette  may  now  be  made  to 
function  as  a  mercury  air-pump  and  the  air  which  is  in  B  can  be 
drawn  over  into  D.  Upon  closing  the  stopcock  g,  raising  the 
bulb  E,  and  then  turning  G  so  that  the  burette  communicates 
with  /,  the  air  which  has  been  drawn  out  of  B  may  be  expelled 
from  the  burette.  This  operation  is  then  repeated  until  no  more 
bubbles  of  gas  appear.  When  the  tube  B  has  thus  been  ex- 
hausted of  air,  the  cocks  a,  b,  and  c  are  opened,  and  the  water 
in  the  apparatus  is  brought  to  boiling  by  heating  the  tubes 
A  and  C  directly  with  the  Bunsen  burner.  The  escape  of  the 
gas  into  the  vacuum  of  B  begins  at  once.  After  about  five  min- 
utes, the  water  in  A  is  brought  nearly  to  the  height  of  the  pinch- 
cock  b  by  raising  or  lowering  the  level-bulb  F.  b  is  then  closed 
and  the  gas  in  B  is  pumped  out  by  raising  and  lowering  the 
level-bulb  E  in  the  manner  above  described.  /  is  connected 
by  means  of  a  bent  capillary  tube  with  a  second  gas  burette  or 
gas  pipette,  and  the  gas  which  has  been  drawn  over  into  D 
from  B  is  transferred  to  the  second  gas  holder  by  turning  g  so 
that  D  communicates  with  /.  The  pinchcock  b  is  then  opened, 
the  water  in  A  is  again  brought  to  boiling,  and  the  gas  set  free 
by  this  second  treatment  is  added  to  the  portion  first  obtained. 
By  repeating  the  process  three  times  it  is  easily  possible  to  com- 
pletely extract  all  of  the  absorbed  gases  with  the  exception 
of  carbon  dioxide.  This  latter  gas  is  so  persistently  retained 


THE  COLLECTION  AND   STORAGE  OF   GASES       21 


by  the  water  that  according  to  the  experiments  of  Jacobsen  it 
is  impossible  to  entirely  remove  it.  Pettersson  has  shown  that 
even  after  strongly  acidifying  the  water  with  sulphuric  acid 
the  carbon  dioxide  cannot  completely  be  driven  out  by 
boiling. 

Collection  of  Gases  from  Reactions  in  Sealed  Tubes.  - 
Gases  are  set  free  in  many  chemical  reactions  that  take  place  in 
sealed  tubes.  If  one 
wishes  to  examine  these 
gases,  Bunsen  directs  1 
that  when  the  tube  is 
fused  together,  it  be 
drawn  out  to  a  fine  tip 
about  2  mm.  wide  and 
50  mm.  long.  To  collect 
the  gases  given  off,  a 
mark  is  made  at  a 
(Fig.  17),  with  a  sharp 
file,  and  the  tip  is  con- 
nected with  a  capillary 
glass  tube  by  means  of 
a  short  piece  of  rubber 
tubing. 

For  safety's  sake  wire 
ligatures  are  put  on  at  b 
and  c.  On  breaking  the  tube  inside  the  rubber  at  a,  the  gas 
passes  through  the  delivery  tube  and  can  be  collected  in  any  de- 
sired receiver.  If  very  strong  pressure  in  the  tube  is  to  be  ex- 
pected, the  rubber  connection  is  surrounded  with  a  strip  of  linen, 
and  the  tube  itself  is  wrapped  in  a  cloth.  A  third  ligature  put 
on  at  d  makes  it  possible  to  stop  the  escape  of  gas  at  any  time, 
the  rubber  forming  with  the  broken-off  glass  tube  a  Bunsen 
rubber  valve. 

Extraction  of  Gases  from  Minerals.  —  To  extract  the  gases 

1  Bunsen,  Gasometrische  Methoden,  2d  ed.,  p.  10. 


FIG.  17 


22 


GAS  ANALYSIS 


that  may  be  present  in  minerals  or  rocks,  Ramsay  and  Travers 1 
recommend  that  the  mineral  first  be  reduced  to  a  fine  powder 
and  be  then  mixed  with  double  its  weight  of  primary  potassium 
sulphate.  The  mixture  is  placed  in  a  hard-glass  tube  which  is 
connected  with  an  air-pump.  After  the  tube  has  been  exhausted 
it  is  heated  to  redness  with  a  large  Bunsen  burner.  The  es- 
caping gases  are  pumped  out  and  are  collected  in  a  small  tube 


FIG.  1 8 

that  contains  a  small  amount  of  a  solution  of 
potassium  hydroxide.  In  order  to  exclude  the 
possibility  of  leakage,  the  tube  is  joined  to  the  air- 
pump  in  the  manner  shown  in  Fig.  18.  As  may 
be  seen  from  the  drawing,  the  large  tube  is  drawn 
out  at  A ,  a  piece  of  rubber  tubing  is  placed  over 
the  end  of  the  small  tube  B,  and  after  it  has  been 

inserted  in  the  contraction  at  A,  the  joint  is  cov- 
FIG.  19 

ered  with  mercury  standing  in  the  wide  portion  C. 

In  most  cases  the  gases  that  are  present  in  the  mineral  are  driven 
out  by  heating  the  substance  alone  without  the  addition  of 
primary  potassium  sulphate. 

To  collect  the  gases  that  are  set  free  when  minerals  are  heated 
in  sealed  tubes  with  sulphuric  acid  Travers  2  uses  the  tube  shown 

1  Proc.  Royal  Soc.,  London,  60  (1896),  442. 
*Proc.  Royal  Soc.,  64  (1898),  132. 


THE  COLLECTION  AND   STORAGE  OF  GASES       23 

in  Fig.  19.  Sulphuric  acid  is  first  poured  into  the  tube  and  the 
weighed  sample  of  the  finely  powdered  mineral  is  placed  in  a 
short  tube  that  has  a  rod  fused  to  the  bottom  of  it  to  hold  this 
sample  tube  above  the  surface  of  the  acid.  This  tube  is  slipped 
into  the  large  tube  in  the  position  shown  in  the  figure,  and  the 
upper  end  of  the  outer  tube  is  then  drawn  out,  is  connected  with 
a  mercury  air-pump  by  means  of  a  rubber  tube,  and  is  exhausted 


FIG.  20 

and  sealed  by  fusion  at  C.  After  the  contents  of  the  tube  has 
been  heated  for  a  length  of  time  sufficient  to  completely  decom- 
pose the  mineral  the  tip  of  the  tube  is  marked  with  a  file  at  D, 
and  the  tube  is  again  attached  to  the  pump  by  a  piece  of  rubber 
tubing.  After  the  air  in  the  connecting  tube  has  been  pumped 
out,  the  tip  C  is  broken  off  inside  the  rubber  tube  and  the  gas 
is  drawn  out  by  means  of  a  mercury  pump  and  is  collected  for 
analysis. 

Gasometers. —  If  a  sample  of  gas  is  to  be  collected  and  kept 
for  analysis  for  a  considerable  length  of  time,  the  portions  of 


24  GAS   ANALYSIS 

the  gas  taken  for  analysis  must  be  displaced  with  mercury. 
Water  may  not  be  used  for  this  purpose  because  its  solvent 
power  for  gases  would  cause  change  in  the  composition  of  the 
gas  mixture.  A  small  gasometer  that  is  suitable  for  prolonged 
storage  of  a  gas  sample  is  shown  in  Fig.  20.  The  large  glass 
bulb  A  serves  to  hold  the  gas.  At  the  top  it  carries  the  bent 


FIG.  21 


FIG,  22 


capillary  tube  a,  and  at  the  bottom  it  is  joined  to  the  level-bulb 
B  by  a  rubber  tube.  The  capillary  is  closed  by  a  rubber  tube  and 
pinchcock.  The  apparatus  is  first  filled  with  mercury.  By 
lowering  or  raising  the  level-bulb,  gas  can  be  drawn  in  or  driven 
out  as  desired.  If  gases  are  to  be  kept  for  some  time,  the  capil- 
lary tube  a  is  filled  with  mercury  by  means  of  a  little  pipette 
inserted  at  c.  This  closes  the  bulb  perfectly. 


THE  COLLECTION  AND   STORAGE  OF   GASES       25 

A  convenient  gasometer  may  easily  be  constructed  from  a 
round-bottomed  flask  fitted  with  a  two-hole  rubber  stopper 
and  bent  glass  tubes  in  the  manner  shown  in  Fig.  21.  The 
thistle  tube  may  be  replaced  by  a  level-bulb  and  rubber  tube 
(see  Fig.  20). 


For  the  collection  and  storage  of  large  samples  of  gas,  gasom- 
eters made  of  sheet  zinc,  of  sheet  iron  or  galvanized  iron, 
or  of  glass  may  be  employed.  The  form  shown  in  Fig.  22  may 
also  be  used  to  aspirate  the  gas  into  the  container.  The  large 


26 


GAS  ANALYSIS 


gasometers  that  ordinarily  are  used  in  laboratories  are  not  well 
adapted  to  the  storage  of  gas  samples  for  analysis  because  of 
the  solvent  action  of  water  upon  the  constituents  of  the  gas  mix- 
ture. This  defect  may  partially  be  remedied  by  using  a  concen- 
trated solution  of  sodium  chlo- 
ride or  of  magnesium  chloride  as 
confining  liquid  or  by  bringing 
a  layer  of  paraffin  oil  upon  the 
surface  of  the  water.1  The 
solvent  action  of  the  confining 
liquid  may  also  be  lessened  by 
using  a  gasometer  of  such  form 
as  will  give  small  surface  of 
contact  between  the  gas  mix- 
ture and  confining  liquid.  An 
instrument  of  this  type  is 
shown  in  Fig.  23. 

The  gasometer  consists  of  the 
bell  A  which  dips  into  the  cylin- 
drical ring-shaped  space  B,  this 
latter  being  filled  with  a  solution 
of  magnesium  chloride.  The 
shaded  part  D  is  a  hollow  cyl- 
inder closed  at  both  the  top 
and  bottom.  The  iron  tube  a 
serves  as  a  guide  for  the  bell 

and  should  therefore  be  made  quite  wide.  The  gasometer  is 
filled  by  introducing  the  gas  in  question  through  /.  A  branch 
tube  at  e  extends  downward  into  a  glass  cylinder  filled  with 
water  and  serves  the  double  purpose  of  enabling  the  op- 
erator to  observe  the  pressure  of  the  gas  and  to  drive  out  any 
air  in  the  tubes  through  this  branch.  The  weights  E  and  F 
make  it  possible  to  regulate  at  will  the  pressure  in  the  gasometer. 

1  See  Voigt,  Chemiker-Zeitung,  32  (1908),  1082,  and  Reinhardt,  Chemiker-Zeitung, 
33  (1909).  206. 


FIG.  24 


THE  COLLECTION  AND  STORAGE  OF  GASES        27 

When  the  gasometer  has  been  filled,  the  rubber  tube  d  is  removed 
from  c.  The  gas  can  then  be  drawn  off  through  either  the  stop- 
cock b  or  c. 

A  glass  gasometer  constructed  on  the  same  principle  as  the 
foregoing  is  shown  in  Fig.  24. 


CHAPTER  II 
THE  MEASUREMENT  OF  LARGE  SAMPLES  OF  GAS 

When  a  gas  is  present  in  a  gas  mixture  in  only  very  small 
amounts,  it  is  usually  determined  by  drawing  or  forcing  a  large 
sample  of  the  gas  mixture  through  a  suitable  absorption  appara- 
tus, and  ascertaining  the  amount  of  the  absorbed  constituent 
by  gravimetric  or  volumetric  means.  It  is  evident  that  under 
such  circumstances  the  large  size  of  the  gas  sample  obviates 
the  necessity  of  very  accurately  determining  its  volume  (see 
page  122). 

An  arrangement  of  apparatus  that  is  suitable  for  the  approxi- 
mate measurement  of  large  gas  volumes,  and  that  can  easily 
be  put  together  from  stock  apparatus  in  the  laboratory,  is  shown 
in  Fig.  25.  The  large  bottle  B  is  filled  with  water,  and  the  stop- 
per carrying  the  inlet  tube  and  the  siphon  tube  D  is  then  in- 
serted in  the  neck  of  the  bottle.  D  is  filled  with  water  by  blow- 
ing into  the  inlet  tube,  and  the  screw  pinchcock  E  is  then  closed. 
B  is  now  connected  with  the  absorption  apparatus  A  through 
which  the  sample  is  to  be  drawn,  and  the  pinchcock  E  is  opened. 
When  the  first  bubble  of  gas  passes  through  the  absorbent,  a 
measuring  cylinder  C  is  placed  under  the  end  of  the  siphon  tube, 
and  the  water  drawn  over  from  the  bottle  B  is  thus  measured. 
After  the  operation  is  complete,  the  volume  of  gas  represented 
by  the  water  that  has  been  measured  off  in  the  cylinder  C  is 
reduced  to  standard  conditions  and  the  percentage  of  the  ab- 
sorbed constituent  in  the  original  gas  volume  is  then  calculated. 

Gas  Meter. —  A  more  convenient  but  more  expensive  appara- 
tus for  measuring  large  gas  volumes  is  an  Experimental  Gas 
Meter  1  of  the  type  shown  in  Fig.  26. 

1  These  meters  may  be  obtained  from  S.  Elster,  Berlin. 

28 


MEASUREMENT  OF  LARGE  SAMPLES  OF  GAS      29 


FIG.  25 


30  GAS  ANALYSIS 

meter  and  is  filled  by  removing  the  cap  M  and  pouring  water 
into  the  opening  until  it  flows  out  of  the  opening  C  in  the  lower 
part  of  the  meter.  The  caps  of  both  openings  are  then  screwed 
firmly  into  place.  The  gas  enters  the  meter  at  F,  passes  through 


FIG.  26 


the  measuring  drums,  and  escapes  through  the  tube  L.  Its 
speed  of  flow  may  be  delicately  adjusted  by  a  micrometer  screw 
that  turns  the  dial  H.  The  manometer  K  shows  the  pressure 
of  the  gas.  The  dial  of  the  meter  is  provided  with  two  hands. 


MEASUREMENT  OF  LARGE  SAMPLES  OF  GAS      31 


FIG.  27 


32  GAS  ANALYSIS 

The  shorter  one  A  records  the  liters  of  gas  that  pass  through 
the  meter.  The  longer  hand  B  makes  one  complete  revolution 
for  every  three  liters  and  is  of  use  in  the  measurement  of  small 
gas  volumes  and  also  in  the  measurement  of  the  amount  of  gas 
passing  through  the  meter  in  a  relatively  short  period  of  time. 

The  Rotameter.  —  A  unique  and  useful  device  for  measuring 
the  volume  of  gas  per  hour  that  is  flowing  through  a  tube  is  the 
rotameter l  shown  in  Fig.  27.  It  consists  of  a  glass  tube  A  through 
which  the  gas  passes  from  below  upward.  The  speed  of  flow  of 
the  gas  current  can  be  regulated  by  turning  the  stopcock  B. 
Inside  the  glass  tube  there  is  a  little  float  F  which  is  carried 
upward  by  the  flowing  gas,  and  at  the  same  time  set  in  rapid 
rotation  about  its  vertical  axis.  The  float  will  rise  or  sink  in 
the  glass  tube  according  to  the  amount  of  gas  t'lat  is  passing 
through  the  tube,  and  the  height  of  the  float,  which  is  measured 
by  a  scale  attached  to  the  tube,  shows  the  number  of  liters  of 
gas  flowing  through  the  tube  per  hour.  The  scale  on  the  tube 
is  an  arbitrary  one,  and  the  instrument  is  calibrated  for  one 
particular  gas.  The  rotameter  is  made  in  different  sizes,  the 
maximum  flow  of  gas  through  the  smallest  size  being  about 
200  liters  per  hour,  and  through  the  largest  size  about  30,000 
liters  per  hour. 

1  This  instrument  may  be  obtained  from  the  Rotawerke,  Aachen,  Germany. 


CHAPTER  III 
THE  MEASUREMENT  OF  GASES 

The  quantity  of  a  gas  may  be  determined  either  by  measuring 
its  volume,  or  by  ascertaining  its  weight,  or  by  causing  it  to  enter 
into  chemical  reactions  that  render  possible  its  determination 
by  indirect  gravimetric  or  volumetric  methods.  Because  of  the 
comparatively  low  densities  of  gases,  the  first  method  is  usually 
most  accurate  as  well  as  most  convenient.  In  fact  in  gas  ana- 
lytic work  the  determination  of  the  amount  of  a  gas  by  direct 
measurement  of  its  weight  is  but  rarely  employed. 

THE  REDUCTION  OF  THE  VOLUME  OF  A  GAS  TO  STANDARD 
CONDITIONS 

The  volume  of  a  gas  is  affected  by  changes  of  pressure  and  of 
temperature. 

The  Law  of  Boyle.  —  The  effect  of  change  of  pressure  is  ex- 
pressed in  the  Law  of  Boyle:  Provided  the  temperature  remains 
constant,  the  volume  of  a  gas  is  inversely  proportional  to  the  pres- 
sure. 

VQ:V  =  p:pQ,  or 

VQpo  =  Vp.  (l) 

The  Law  of  Charles.  —  If  a  gas  at  o°  C.  be  warmed  to  i°  C. 
(the  pressure  remaining  constant)  it  will  expand  ^TT  °f  the  vol- 
ume that  it  occupied  at  o°.  If  the  temperature  of  the  gas  be 
raised  from  o°  to  273°,  its  volume  will  double.  Similarly,  if  a 
gas  be  cooled  below  o°,  its  volume  will  decrease  ^-§-  of  its  vol- 
ume at  o°  for  each  degree  of  fall  of  temperature  below  o°. 
These  facts  are  briefly  stated  in  the  Law  of  Charles:  Provided 

33 


34'  GAS  ANALYSIS 

the  pressure  remains  constant,  the  volume  of  a  gas  will  change 
-g-y-g-  or  0.00367  of  its  volume  at  o°  for  each  degree  of  change  of 
temperature.  If  z>0  represent  the  volume  of  the  gas  at  o°  and  v 
the  volume  at  a  temperature  t  and  a  =  YTS> 


v  =  vQ  (i  +  a/),  or 

|I|ii  1     *°=rr^  "  •  (2) 

Similarly,  the  volume  v\  of  the  gas  at  a  temperature  t\  would 
from  (2)  be 

>  or 
Consequently, 


+  o/i 

Vi 


Furthermore,  if  the  volume  of  a^gas  remains  constant,  its  pres- 
sure will  change  ^\^  or  0.00367  of  its  pressure  at  o°  for  each  degree 
of  change  in  temperature. 

p  =  po  (i  +  at) 

or 


pi  =  po  (i  +  d/i)   or 

po  ' 

i    -t-  "*i 

v>, 

(4) 

Since  the  effect  of  change  of  temperature  is  represented  by 
the  same  formula  whether  pressure  or  volume  is  under  con- 


THE  MEASUREMENT  OF   GASES  35 

sideration,  by  combining  (3)  and  (4)  there  is  obtained  the  ex- 
pression 

(  } 


i  +  at       i  +  o/i 

In  stating  the  volume  of  a  gas  it  is  agreed  among  scientists 
to  express  it  in  terms  of  the  volume  that  the  gas  would  occupy 
under  certain  arbitrary  conditions  (standard  conditions)  namely 
—  at  a  temperature  of  o°  C.  and  under  a  pressure  of  760  mm.  of 
mercury.  To  reduce  an  observed  gas  volume  to  the  volume 
that  it  would  occupy  under  standard  conditions  we  may  employ 
the  formula  (5).  Since 


it  must  also  be  true  that 
.    If  now  po  =  760  and  to  =  O°  C. 


i  +  at0      i+  at 
then  since  a  =  0.00367 

vp 

VQ  760  =  — —    or 

i  +  0.00367^ 

VQ  =  v— — ; — r  (6)   in  which  VQ 

760(1  +0.003670 

is  the  volume  under  standard  conditions,  z>  the  observed  volume, 
p  the  observed  pressure  expressed  in  millimeters  of  mercury 
and  t  the  observed  temperature. 

By  means  of  the  above  formula  (6)  a  gas  volume  may 
correctly  be  reduced  to  standard  conditions  provided  the  gas, 
when  measured,  contains  no  water  vapor.  If,  however,  water 
vapor  is  present,  a  correction  must  be  introduced.  Every 
liquid  tends  to  change  to  the  gaseous  state  and  the  vapor  of  the 
liquid  exerts  a  gas  pressure  which  is  termed  the  vapor  pressure 
of  the  liquid.  This  vapor  pressure  is  dependent  upon  the  temper- 


36  GAS  ANALYSIS 

ature  and  upon  the  nature  of  the  liquid,  but  it  is  not  affected  by 
the  pressure  of  other  gases,  nor  by  the  amount  of  the  liquid 
that  is  present.  If  a  closed  space  is  filled  with  a  mixture  of  gases, 
each  gas  will  exert  a  definite  pressure  which  is  the  same  whether 
it  exists  alone  in  the  space  or  whether  other  gases  are  present. 
The  total  pressure  of  the  gas  mixture  is  the  sum  of  the  partial 
pressures  of  the  various  gases.  If  now  a  gas  volume  that  con- 
tains water  vapor  is  measured  at  atmospheric  pressure,  the 
partial  pressure  of  the  dry  gas  will  equal  the  barometric  pressure 
less  the  pressure  of  the  water  vapor  in  the  gas.  If  the  gas  is  not 
" saturated"  with  water  vapor,  the  partial  pressure  of  the  latter 
is  difficult  to  determine.  But  when  a  gas  is  measured  over  water, 
or  over  mercury  upon  which  stands  a  small  amount  of  water,  the 
space  is  saturated  with  water  vapor,  and  since  the  maximum 
pressure  of  water  vapor  at  various  temperatures  is  known  (see 
table  on  p.  411)  the  pressure  of  the  dry  gas  can  easily  be  ascer- 
tained by  noting  the  temperature  of  the  gas  and  subtracting 
from  the  observed  barometric  pressure  the  pressure  of  water 
vapor  at  the  observed  temperature.  Representing  the  pressure 
of  the  water  vapor  by  m,  and  inserting  this  correction  in  formula 
(6),  we  obtain 

p  —  ™  /  , 

760  (  i  +  0.00367/ ) 

Inasmuch  as  the  vapor  pressures  of  liquids  vary  with  the  na- 
ture of  the  liquids,  it  is  apparent  that  if  a  gas  is  measured  over 
a  liquid  other  than  pure  water  the  correction  to  be  introduced 
for  the  vapor  pressure  of  the  liquid  will  not  be  the  same  as  for 
that  of  pure  water.  For  this  reason  those  forms  of  apparatus  in 
which  gas  volumes  are  measured  over  concentrated  solutions  of 
various  absorbents  will  not  yield  accurate  results  unless  the  vapor 
pressure  of  each  solution  is  known  and  taken  into  account.  To 
avoid  error  from  this  source  it  is  now  customary,  in  the  better 
types  of  apparatus,  to  pass  the  gas  mixture  from  a  measuring 
burette  into  a  separate  apparatus  containing  the  absorbent, 


THE  MEASUREMENT  OF  GASES 


37 


and  to  then  draw  the  gas  back  into  the  burette  where  it  comes 
into  contact  with  water  before  being  again  measured.  In  this 
manner  the  space  occupied  by  the  gas  is  always  saturated  with 
water  vapor  when  the  volume 
of  the  gas  is  measured. 

When  a  gas  is  measured 
over  dry  mercury,  the  vapor 
pressure  of  the  mercury  is  so 
small  as  to  be  negligible  un- 
less the  gas  is  measured  at 
a  temperature  considerably 
above  40°. 

THE   LUNGE    GAS    VOLUMETER 

To  facilitate  work  with  the 
nitrometer  (p.  397)  Lunge  has 
devised  an  instrument,  the 
gas  volumeter,  with  the  aid 
of  which  a  volume  of  gas  in 
the  measuring  tube  of  the 
apparatus  may  quickly  be 
brought  to  the  volume  that 
it  would  occupy  under  stand- 
ard conditions.  This  does 
away  with  the  usual  calcula- 
tions and  effects  a  consider- 
able saving  of  time. 

The  instrument,  Fig.  28, 
consists  of  a  gas  burette  A, 
a  reduction  tube  B,  and  a 
level-tube  C,  which  are  con- 
nected at  the  lower  ends  by 
pieces  of  enamelled  rubber 
tubing  and  the  T  tube  D. 

The  gas  burette  A  has  a 


3  8  GAS  ANALYSIS 

capacity  of  somewhat  more  than  100  cc.  and  is  calibrated  from 
the  stopcock  downward  in  100  cc.  divided  into  f  cc.  At  its 
upper  end  is  a  two-way  stopcock  S.  The  upper  tubes  of  the 
stopcock  are  capillary  and  one  of  them  is  bent  over  and  down- 
ward as  shown  in  the  figure. 

The  reduction  tube  B  is  provided  with  a  single  bore  stopcock 
at  the  upper  end.  Below  the  stopcock  it  is  widened  into  a 
bulb.  From  the  stopcock  to  a  mark  on  the  tube  somewhat  be- 
low the  bulb  the  tube  holds  exactly  100  cc.  From  the  100  cc. 
mark  downward  the  tube  is  calibrated  to  about  140  cc.  in  ^  cc. 

The  level-tube  C  is  a  plain  tube  open  at  the  top.  The  three 
tubes  are  fastened  in  clamps  that  are  attached  to  the  iron 
stand  H. 

To  prepare  the  apparatus  for  use  it  is  first  necessary  to  inclose 
in  the  reduction  tube  a  volume  of  moist  air  that,  under  standard 
conditions  and  in  the  dry  state,  would  have  a  volume  of  exactly 
100  cc.  This  is  accomplished  as  follows: — 

The  apparatus  is  filled  with  clean  mercury  and  somewhat 
more  than  100  cc.  of  air  is  then  drawn  into  the  reduction  tube 
B  by  opening  the  stopcock  of  the  tube  and  lowering  the  level- 
tube  C.  A  drop  of  water  is  next  drawn  into  the  bulb  of  B  through 
the  stopcock  to  insure  that  the  space  above  the  mercury  in  the 
reduction  tube  is  saturated  with  water  vapor.  A  thermometer 
is  hung  close  to  the  apparatus,  and  after  the  apparatus  has 
come  to  the  temperature  of  the  room,  the  thermometer  and 
barometer  are  carefully  read. 

The  volume  that  100  cc.  of  air,  under  standard  conditions, 
would  occupy  under  the  observed  temperature  and  pressure 
is  now  calculated  from  the  formula 

760(1  +.003670 

V    =  VQ  

p  —  m 
which  is  derived  directly  from  (7)  on  p.  36,  and  in   which 

VQ  =   100  CC. 

The  stopcock  of  the  reduction  tube  is  now  opened,  and  the 


THE  MEASUREMENT  OF  GASES  39 

level-tube  is  raised  or  lowered  until  the  mercury  in  B  stands 
exactly  at  the  volume  calculated  for  v.  The  stopcock  of  B  is 
then  closed.  There  is  thus  inclosed  in  the  reduction  tube  a 
volume  of  air  that  will  occupy  exactly  100  cc.  when  measured 
under  standard  conditions. 

If  now  a  gas  is  brought  into  the  burette  A,  the  volume  that 
it  would  occupy  under  standard  conditions  may  rapidly  be 
ascertained  in  the  following  manner. 

The  level-tube  C  is  raised  or  lowered  until  the  mercury  in 
the  reduction  tube  B  stands  close  to  the  100  cc.  mark,  and 
C  is  then  clamped  firmly  in  that  position.  The  burette  A  is 
now  raised  or  lowered  until  the  mercury  in  it  stands  at  the  same 
height  as  that  in  the  reduction  tube  and  it  is  then  clamped  in 
position.  This  adjustment  will  usually  cause  the  mercury  to 
move  up  or  down  from  the  100  cc.  mark  in  B.  It  is  brought 
back  to  the  mark  by  again  changing  the  height  of  the  level-tube 
and  the  burette  is  again  raised  or  lowered  until  the  mercury 
in  it  and  in  B  are  at  the  same  level.  These  adjustments  are 
repeated  until,  with  the  mercury  in  A  and  B  at  the  same  height, 
the  mercury  in  the  reduction  tube  B  stands  exactly  at  the  100  cc. 
mark. 

Since  the  pressure  upon  the  air  in  B  suffices  to  bring  it,  at 
the  now  prevailing  temperature,  to  the  volume  that  it  would 
occupy  under  standard  conditions,  it  follows  that  the  gas  in  the 
burette  A *,  if  at  the  same  temperature  as  the  air  in  B,  will  also 
be  brought  to  the  volume  that  it  would  occupy  under  standard 
conditions,  and  consequently  its  corrected  volume  may  be 
directly  read  off. 

The  Lunge  gas  volumeter  is  open  to  criticism  because  the 
burette  and  the  reduction  tube  stand  free  in  the  air  and  for 
that  reason  are  subject  to  sudden  and  different  changes  of  tem- 
perature. This  may  cause  appreciable  error  since  a  difference 
of  only  i°  C.  would  mean  a  variation  of  0.3  per  cent  in  the  gas 

1  The  space  above  the  mercury  in  A  must  be  course  of  saturated  with  water  vapor 
as  is  the  space  in  B. 


40  GAS  ANALYSIS 

volume.  For  this  reason  the  apparatus  will  give  dependable 
results  only  when  it  stands  in  a  room  of  uniform  temperature 
and  free  from  drafts,  and  when  in  the  manipulation  great  care 
is  exercised  to  avoid  the  uneven  warming  of  the  tubes  by  heat 
from  the  hands  or  from  the  body  of  the  operator. 

THE  BODLANDER   GAS   BAROSCOPE 

Bodlander  has  devised1  an  ingenious  instrument  with  the 
aid  of  which  the  weight  of  the  gas  in  the  measuring  burette  may 
be  calculated  in  very  simple  manner  from  its  pressure. 

A  volume  of  gas  v  that  is  measured  at  f  and  under  a  pressure 
of  p  mm.  may  be  reduced  to  the  volume  that  it  would  occupy 
under  standard  conditions  v0  according  to  the  equation 

VX  p  X  273 


760  (273  +  /) 

Since  the  weight  of  a  cubic  centimeter  of  a  gas  of  the  molecu- 
lar weight  M  is  equal  to  0.0446725  X  M  mg.,  the  weight  G  of 
i)  cc.  of  the  gas 

v  X  p  X  273  X  0.0446725  X  M 
G  =  -         -  —  —  -  -  -  mg.  (i) 

760  (273  +  /) 

If  in  all  of  the  measurements  the  volume  is  adjusted  so  that 

760  (273  +  /) 

v  =  --  -  -  cc.  (2) 

273   x  0.0446725   x  100 

then  equation  (i)  may  be  reduced  to  the  simple  form 

pxM 

G  =  -    -mg  (3) 

100 

If  now  an  apparatus  is  so  constructed  and  calibrated  that  the 
volume  of  a  gas  corresponding  to  equation  (2)  at  a  prevailing 
temperature  of  /°  may  easily  be  ascertained,  then  the  wreight 
1Z.f.  angew.  Chem.,  1894,  425. 


THE   MEASUREMENT  OF   GASES 


of  the  gas  in  milligrams  may  be 
determined  by  bringing  the  gas  to 
this  volume,  ascertaining  the  pres- 
sure exerted  by  the  gas,  and  multi- 
plying this  pressure,  expressed  in 
decimeters,  by  the  molecular 
weight  of  the  gas. 

The  instrument  that  Bodlander 
devised  for  this  style  of  analysis 
is  termed  by  him  a  gas  baroscope. 
The  essential  parts  of  the  appara- 
tus are  shown  in  Fig.  29.  The 
measuring  tube  consists  of  the 
bulb  A  which  is  about  7  cm.  in 
diameter,  and  a  tube  B  on  which 
is  marked  a  scale  running  from 
zero  at  the  top  to  30  near  the  bot- 
tom, each  division  being  divided 
into  fifths.  A  and  B  are  sur- 
rounded by  a  water  mantle.  The 
upper  end  of  the  tube  is  closed  by 
the  two-way  stopcock  S  that  ends 
in  the  capillaries  C  and  D.  The 
capacity  of  the  measuring  tube 
from  the  lower  side  of  the  stopcock 
to  the  mark  zero  on  the  tube  B  is 
the  volume  at  o°  calculated  from 
equation  (2)  when  /  =  o.  The  vol- 
ume down  to  division  one  is  that 
at  i°  calculated  for  /  =  i,  and  so  on. 

The  lower  end  of  the  measuring 
tube  B  is  connected  by  a 
piece  of  enamelled  rubber 

tubing  with  the  level-bulb 

L  which  is  provided  with 


G- 


FIG. 


2Q 


42  GAS  ANALYSIS 

a  stopcock  F  and  a  bent  tube  G  that  is  about  12  mm.  internal 
diameter  and  projects  about  27  cm.  above  the  bulb.  The  con- 
tents of  L  is  somewhat  greater  than  that  of  the  bulb  A.  The 
measuring  tube  and  the  level-bulb  are  fastened  by  clamps  to 
an  iron  stand  M  that  is  about  1.2  meter  high.  The  level-bulb 
L  and  the  clamp  that  carries  it  may  be  slid  up  and  down 
upon  the  rod  in  such  manner  that  the  tube  G  of  the  bulb  lies 
close  to  the  front  of  a -meter  scale  K  that  is  divided  into  milli- 
meters and  hangs  in  a  perpendicular  position  from  a  clamp  at- 
tached near  the  upper  end  of  the  rod. 

The  measurements  with  the  gas  baroscope  are  made*in  the 
following  manner.  The  instrument  is  filled  with  clean  mercury. 
The  air  in  the  bulb  A  is  completely  driven  out  through  the  capil- 
lary tube  C  by  opening  the  stopcock  S  and  raising  the  level-bulb. 
The  capillary  tube  D  is  then  connected  with  the  evolution  ap- 
paratus or  the  container  that  holds  the  gas  that  is  to  be  measured 
and  the  gas  is  drawn  into  the  bulb  A  by  turning  the  stopcock  5" 
to  proper  position  and  lowering  the  level-bulb  L.  S  is  then  closed 
and  the  level-bulb  L  is  lowered  until  the  gas  in  A  and  B  is  ex- 
panded to  such  a  volume  that  the  mercury  in  B  stands  at  the 
mark  on  the  scale  that  corresponds  to  the  prevailing  tempera- 
ture. The  sharp  adjustment  of  the  mercury  to  this  mark  is  ac- 
complished by  lowering  L  until  the  mercury  in  B  stands  some- 
what below  the  mark,  and  then  turning  down  the  clamp  H 
upon  the  rubber  tube  until  the  mercury  is  brought  exactly  to 
the  proper  height.  The  apparatus  must  contain  such  an  amount 
of  mercury  that  this  will  now  stand  in  the  tube  G  above  the 
level-bulb.  G  itself  stands  close  to  the  scale  K,  but  should  not 
be  allowed  to  touch  the  scale  and  thus  push  it  out  of  its  per- 
pendicular position.  The  height  of  the  mercury  in  G  is  now 
carefully  read  off  on  the  scale  K  with  the  naked  eye.  This 
reading  can  be  made  to  an  accuracy  of  about  one-tenth  mm. 
but  the  readings  are  of  course  more  accurate  if  made  with  a 
cathetometer. 

To  ascertain  the  pressure  exerted  by  the  gas  in  A  a  second 


THE  MEASUREMENT  OF  GASES  43 

reading  is  necessary.  The  gas  is  first  driven  out  of  A  through 
the  capillary  tube  C  by  opening  S  and  raising  the  level-bulb. 
S  is  then  closed  and  L  is  lowered  until  the  mercury  in  the  tube  B 
stands  at  exactly  the  same  position  as  before.  The  height  of  the 
mercury  in  G  is  then  read  off  upon  the  scale,  and  the  difference 
between  this  reading  and  the  first  reading  on  the  scale  expressed 
in  decimeters  and  multiplied  by  the  molecular  weight  of  the  gas 
gives  the  weight  of  the  gas  in  milligrams. 

If  a  mixture  of  gases  has  first  been  introduced  into  the  measur- 
ing tube  and  the  weight  of  a  constituent  gas  is  desired,  the 
pressure  of  the  gas  mixture  is  first  ascertained  in  the  manner 
above  described,  the  capillary  tube  C  is  then  connected  with  a 
suitable  absorption  pipette  for  the  removal  of  the  constituent 
in  question,  the  gas  mixture  is  driven  over  into  this  pipette  and 
is  then  drawn  back  into  A.  The  mercury  in  B  is  now  again 
brought  to  the  original  mark,  the  pressure  is  read,  and  from 
the  difference  in  pressure,  the  weight  of  the  absorbed  constituent 
is  calculated. 

If  the  gas  that  is  being  measured  is  saturated  with  moisture, 
a  drop  or  two  of  water  should  be  introduced  into  A  upon  the 
mercury  before  the  final  measurement  of  the  pressure,  after 
the  removal  of  the  gas,  is  made.  No  correction  for  the  tension 
of  water  vapor  is  then  necessary. 


CHAPTER  IV 

THE  DETERMINATION  OF  THE  SPECIFIC  GRAVITY  OF 

A  GAS 

The  determination  of  the  specific  gravity  of  a  gas  may  con- 
veniently be  made  by  Bunsen's  method  l  of  measuring  the  time 
of  escape  of  the  gas. 

This  method  is  based  upon  the  fact  that  the  specific  gravities 
of  two  gases-  escaping  through  small  openings  in  thin  plates  bear 
nearly  the  same  ratio  to  each  other  as  the  squares  of  their  times 
of  escape.  If  a  gas  of  the  specific  gravity  s  has  a  time  of  flow  /, 
and  another  gas  'of  a  specific  gravity  si  has  a  time  of  flow  /i, 
the  relation  between  the  time  of  escape  and  the  specific  gravity 
is  given  by  the  equation  — 

si_      t£ 

s      "    t2' 

If  s  or  the  specific  gravity  of  one  of  the  gases  be  regarded  as  i  , 
the  specific  gravity  of  the  other  gas  is  found  by  the  formula  — 


51  " 


Figure  30  shows  the  apparatus  used  for  this  determination. 
A  glass  tube  of  about  70  cc.  capacity  is  luted  into  the  iron 
cap  A  .  This  cap  is  fitted  with  a  three-way  stopcock  by  means  of 
which  the  inside  of  the  glass  tube  can  be  brought  into  communi- 
catiqn  with  either  the  tube  B  through  which  the  gases  are  in- 
troduced, or  the  small  opening  in  C.  This  opening  is  made  in  a 
platinum  plate,  which  is  about  as  thick  as  tin  foil,  and  is  luted 
in  position.  To  obtain  an  opening  as  small  as  needed,  the 

1  Bunsen,  Gasometrische  Methoden,  2d  ed.,  p.  184. 
44 


DETERMINATION  OF  SPECIFIC   GRAVITY   OF   GAS  45 


platinum  foil  is  pierced  with  a  fine  sewing  needle,  and  is 
hammered  with  a  polished  hammer  upon  a  polished  anvil 
until  the  opening  can  no  longer  be  seen  with  the  naked  eye, 
and  is  visible  only  when  the  plate  is  held  between  the  eye 
and  a  bright  flame.  The  plate  thus  perforated  is  cut  out  in 
the  form  of  a  small  circular  disk,  the 
opening  being  at  the  center. 

In  order  that  the  gases  to  be  ex- 
amined may  always  escape  through 
the  opening  C  under  the  same  con- 
ditions as  regards  pressure,  there  is 
placed  in  A  a  float  bb.  This  float 
should  be  as  light  as  possible,  and  for 
this  reason  it  is  best  made  from  a  very 
thin-walled  glass  tube.  The  float  has 
at  /3  a  little  button  of  black  glass 
from  which  projects  a  small,  white 
glass  point. 

Two  fine  threads  of  black  glass,  fii 
and  y8-2,  are  fused  around  the  lower 
part  of  the  stem  of  the  float.  These 
two  threads,  together  with  the  black 
glass  button  at  the  top,  serve  as 
marks. 

If  the  tube  containing  the  gas  be 
pushed  down  so  far  into  the  mercury 
that  a  mark  on  the  glass  is  tangent  to 


FIG.  30 


the  outer  mercury  surface,  then  the  float  which  is  inside  the  tube 
is  no  longer  visible  through  the  telescope. 

If  now  the  stopcock  be  opened  and  the  gas  allowed  to  escape 
through  the  opening  in  the  platinum  plate,  the  float  rises,  being 
carried  up  upon  the  surface  of  the  mercury  in  the  tube.  If  the 
level  of  the  external  mercury  be  observed  through  the  telescope, 
the  white  glass  tip  of  the  float  soon  comes  into  the  field,  and  in- 
forms the  observer  that  the  black  button  {$  will  shortly  appear. 


46 


GAS  ANALYSIS 


When  this  comes  in  sight  the  time  is  taken,  the  end  of  the  timing 
being  at  that  moment  at  which  the  mark  ^82  comes  into  the  field 
of  the  telescope;  the  near  approach  of  ^82  is  here  shown  by  the 
appearance  of  j8i. 

From  these  observations  is  obtained  the  time  of  escape  of  a 
column  of  gas  which,  measured  from  /3,  has  the  length  shown 

by  the  marks  $82  on  the  float; 
moreover,  the  gases  escape  under 
the  same  differences  of  pressure  in 
all  of  the  experiments.  The  times 
taken  by  the  different  gases  to 
escape  through  the  fine  opening  in 
C  give,  when  squared,  the  ratios  of 
the  specific  gravities  of  the  gases. 

The  gases  must  be  dried,  and  the 
mercury  must  be  pure  and  dry. 
An  advantage  of  the  Bunsen  ap- 
paratus is  that  a  determination  can 
be  made  with  a  very  small  quantity 
of  the  gas. 

Schilling  has  given  the  apparatus 
a  very  practical  form  for  the  ex- 
amination of  illuminating  gas, 
where  large  amounts  of  the  gas 
are  usually  available. 

A  (Fig.  31)  is  a  glass  tube  of  40 
mm.  internal  diameter  and  about 

450  mm.  long.     The  upper  end  is 

luted  into  a  brass  cover  C  into 
which  is  inserted  the  tube  B 

through  which  the  gas  is  led  in.  The  gas  escapes  through  a  per- 
forated platinum  disk  in  the  upper  end  of  the  tube  D.  A  ther- 
mometer T  is  immersed  in  the  water  of  the  cylinder  K.  The 
inner  cylinder  has  two  marks,  M  and  N.  The  apparatus  is 
filled  with  water. 


FIG.  31 


DETERMINATION  OF  SPECIFIC  GRAVITY  OF  GAS    47 


To  determine  the  specific  gravity  of  an  illuminating  gas  with 
this  apparatus,  the  tube  is  first  filled  with  air,  and  the  time  of 
escape  of  the  air,  under  the  prevailing  temperature  and  pressure, 
is  noted.  The  last  trace  of  air  is  then  removed  by  repeatedly 
drawing  in  and  driving  out  the 
gas  to  be  examined,  and  the  time 
of  escape  of  the  illuminating  gas 
is  then  observed.  The  squares 
of  the  values  are  directly  pro- 
portional to  the  specific  grav- 
ities of  the  gases.  Since  the 
specific  gravity  of  air  is  usually 
taken  as  i,  the  calculation  is 
very  simple. 

The  Schilling  apparatus  is 
open  to  objection  because  of  the 
inconvenience  in  filling  the  inner 
cylinder  with  the  gas  under 
examination.  Moreover,  the 
marks  are  so  far  apart  as  to  ren- 
der the  reading  of  them  some- 
what awkward.  These  draw- 
backs are  avoided  in  the  mod- 
ification of  the  apparatus 
devised  by  Pannertz,1  who  uses 
two  glass  bulbs  that  are  con- 
nected by  a  piece  of  rubber 
tubing  (Fig.  32).  The  measure- 
ments are  made  with  the  flask  at  the  right  which  has  an  iron 
cap  C  of  the  same  general  construction  as  that  used  with  the 
Bunsen  apparatus.  The  two  marks  A  and  B  are  placed  upon 
the  narrow  necks  of  the  bulb.  The  flask  is  filled  with  air  or 
with  the  gas  mixture  by  first  raising  the  level  bulb  and  filling 
the  measuring  bulb  with  water  and  then  placing  the  measuring 

1  /./.  Gasbeleuchtung,  48  (1905),  901. 


FIG.  32 


48  GAS  ANALYSIS 

bulb  on  the  stand  D  and  drawing  in  the  air  or  gas  through  the 
side  arm  of  the  iron  cap.  In  measuring  the  time  of  escape  of 
the  air  or  gas,  the  measuring  vessel  is  placed  upon  the  stand  E 
and  the  level  bulb  is  placed  upon  the  stand  D  as  shown  in  the 
figure.  When  the  apparatus  is  charged  with  the  right  amount 
of  water,  the  water  will  rise  above  the  upper  mark  B  nearly 
to  the  iron  cap. 


CHAPTER  V 

ARRANGEMENT  AND  FITTINGS  OF  THE 
LABORATORY 

The  room  for  gas  analysis  should  have  a  northern  exposure 
and  should  have  wide  windows.  The  working-table  should 
run  along  the  outer  wall  so  that  the  operator  may  face  the  win- 
dow and  be  able  to  make  his  readings  without  being  obliged  to 
turn  around  toward  the  source  of  light.  The  floor  should  be 
of  cement,  and  should  slope  slightly  toward  the  middle  in  order 
that  any  mercury  that  may  be  spilled  may  easily  be  brought 
together  and  taken  up.  If  the  floor  is  of  wood,  it  may 
be  made  mercury-tight  by  covering  it  with  linoleum.  The 
room  should  further  be  provided  with  gas  and  with  running 
water  and  with  a  large  sink.  The  sink  should  have  an  iron 
"S"  trap,  and  the  lower  bend  of  this  trap  should  be  bored, 
threaded,  and  provided  with  a  screw  plug  to  permit  of  the  easy 
removal  of  any  mercury  that  may  collect  in  the  trap. 

There  should  also  be  an  ample  supply  of  water  of  the  tempera- 
ture of  the  room.  It  is  convenient  to  have  this  water  piped  to 
every  working-place.  This  is  cheaply  accomplished  by  plac- 
ing near  the  top  of  the  room  and  above  the  sink  a  galvanized 
iron  tank  containing  100  liters  or  more,  and  running  from 
the  lower  part  of  this  tank  an  iron  pipe  that  passes  along 
the  tables.  The  tank  is  easily  filled  through  a  small  iron  pipe 
which  hooks  over  its  top  and  reaches  down  into  the  sink, 
where  it  may  be  connected  with  the  faucet  by  a  piece  of  rubber 
tubing. 

The  laboratory  should  also  contain  a  mercury  air-pump,  a 
barometer,  accurate  thermometers,  and  water  suction-pumps 
at  the  working-tables.  An  electric  current  is  necessary,  and 

49 


50  GAS  ANALYSIS 

this  may  be  supplied  either  by  a  battery  or  storage  cells,  or 
the  direct  current  from  a  dynamo  may  be  utilized.  A  small 
induction  coil  is  needed  for  analysis  of  gas  mixtures  by  explo- 
sion. It  is  desirable  to  have  narrow  shelves  fastened  to  the 
wall  upon  which  to  place  the  Hempel  pipettes. 


CHAPTER  VI 

APPARATUS  FOR  GAS  ANALYSIS  WITH  WATER  AS  THE 
CONFINING  LIQUID 

THE  HEMPEL  SIMPLE  GAS  BURETTE  (Fig.  33)  1 

This  consists  of  two  glass  tubes,  A  and  B,  which  are  set  in 
iron  feet,  F  and  D,  and  are  connected  by  a  rubber  tube  of  7  mm. 
internal  diameter,  12  mm.  external  diameter,  and  about  120  cm. 
long.  To  facilitate  the  cleaning  of  the  burette  the  rubber  tube 
may  be  divided  in  the  middle  and  the  two  ends  joined  by  a 
piece  of  glass  tubing. 

Inside  the  feet  the  tubes  A  and  B  are  bent  at  right  angles 
and  conically  drawn  out.  The  end  projecting  from  the  iron 
is  of  about  4  mm.  external  diameter  and  is  somewhat  corrugated, 
so  that  a  rubber  tube  may  be  tightly  fastened  to  it  by  wire 
ligatures. 

The  measuring  tube  A  ends  at  the  top  in  a  capillary  tube  C 
of  i  mm.  internal  diameter,  6  mm.  external  diameter,  and  about 
3  cm.  long.  Over  this  a  short  piece  of  soft  rubber  tubing, 
3  mm.  internal  diameter,  and  6.5  mm.  external  diameter,  is 
wired  on.  The  rubber  tube  is  closed  by  a  Mohr  pinchcock  E 
which  is  put  on  close  to  the  end  of  the  capillary.  Originally 
the  burette  terminated  in  a  glass  stopcock,  but  this  renders 
the  apparatus  fragile  and  costly.  If  the  apparatus  is  properly 
manipulated  during  the  analysis  the  rubber  tube  does  not  come 
in  contact  with  more  than  traces  of  the  absorbent  and  will  re- 
main in  good  condition  for  a  considerable  length  of  time.  It 
should,  however,  be  tested  from  time  to  time  to  see  that  it  is 
tight.  The  pinchcock  should  always  be  taken  off  from  the 

1  The  Hempel  apparatus  for  technical  gas  analysis  is  excellently  constructed  by 
Greiner  and  Friedrichs  of  Stiitzerbach  in  Thiiringen,  Germany. 

51 


GAS  ANALYSIS 


rubber  tube  after  using  as  this  helps  much  to  keep  the  latter 
in  good  condition.  Notwithstanding  the  fact  that  readings 
cannot  be  made  under  the  rubber  tube,  no  measurable  error  re- 


B 


FIG.  33 


GAS  ANALYSIS  OVER  WATER  53 

suits  therefrom,  since  the  internal  diameter  of  the  glass  tube  C 
is  very  small.  The  differences  in  volume  are  much  less  than  a 
tenth  of  a  cubic  centimeter,  a  variation  which,  in  determina- 
tions not  made  over  mercury,  may  be  entirely  disregarded.  The 
graduated  measuring  tube  A  contains  100  cc.,  the  lowest  mark 
being  slightly  above  the  iron  foot.  The  cubic  centimeters  are 
divided  into  fifths,  and  the  numbers  run  both  up  and  down. 
The  level-tube  B  is  somewhat  widened  at  the  upper  end  to 
facilitate  the  pouring  in  of  the  confining  liquid. 

In  the  Hempel  method  of  gas  analysis  the  absorbable  constit- 
uents of  a  gas  mixture  are  successively  removed  by  passing 
the  gas  into  a  series  of  gas  pipettes  containing  suitable  reagents. 
The  construction  of  these  pipettes  is  such  as  to  render  it  possible 
to  bring  the  gases  into  intimate  contact  with  the  absorbents. 
The  pipette  may  even  be  disconnected  from  the  burette  and 
vigorously  shaken.  There  must  be  at  least  as  many  pipettes  as 
there  are  absorbable  constituents  in  the  gas  mixture. 

The  following  forms,  varied  to  suit  the  nature  of  the  different 
reagents,  are  used: 

THE  HEMPEL   SIMPLE  ABSORPTION  PIPETTES 

These  are  modifications  of  the  Ettling  gas  pipette,  first  used 
by  Doyere  for  the  absorption  of  gases,  and  they  are  filled  with 
such  absorbing  liquids  as  are  not  affected  by  the  air. 

The  Hempel  Simple  Absorption  Pipette  for  Liquid  Reagents 

It  consists  of  two  large  bulbs,  a  and  b  (Fig.  34),  joined  by  the 
tube  d,  and  of  a  capillary  glass  tube  c  of  i  mm.  internal  diameter, 
and  6  mm.  external  diameter  and  bent  as  shown  in  the  figure. 
The  distance  h  must  be  greater  than  g  to  render  it  possible  to 
inclose  a  gas  between  two  columns  of  liquid  in  the  pipette. 

The  bulb  a  holds  about  100  cc.,  and  b  about  150  cc.,  so  that 
when  100  cc.  of  gas  is  brought  into  b,  sufficient  space  for  the 
absorbing  liquid  will  remain.  To  protect  the  pipette  from 


54 


GAS  ANALYSIS 


being  broken  and  to  facilitate  its  manipulation,  it  is  fastened 
to  a  wooden  or  iron  stand. 

An  iron  stand  is  preferable  to  wood  because  its  greater  weight 
renders  it  more  stable  and  because  it  cannot  warp  out  of  shape. 
An  iron  stand  with  a  four-sided  base  is  superior  to  one  with  legs 
only  at  the  ends  because  with  the  latter  form  of  base  there  is 
danger  that  one  leg  of  the  pipette  may  be  pushed  over  the 

edge  of  the  stand  (see 
Fig.  38)  and  the  appara- 
tus fall  and  be  broken. 

The  pipette  is  fastened 
in  the  iron  standard  at  the 
three  points  shown  in  Fig. 
34.  The  capillary  tube 
and  the  tube  above  a  are 
slipped  through  openings 
in  the  upper  bar  of  the 
frame  and  the  tube  below 
b  is  set  back  against  the 
lower  cross-bar.  The  small 
plate  that  closes  this  lower 
opening  is  then  fastened 
in  place  by  screws,  and 
the  spaces  between  the 
three  tubes  and  their  iron 


& 


FIG.  34 


collars  are  filled  with  Plaster  of  Paris.  It  is  well  to  bring  the 
Plaster  of  Paris  up  around  the  lower  part  of  b  for  the  purpose 
of  giving  the  bulb  additional  support.  If  the  pipette  is  broken, 
the  plate  is  unscrewed,  the  glass  parts  and  the  Plaster  of 
Paris  are  broken  out  and  a  new  pipette  is  slipped  into  place 
and  fastened  as  above  described.  With  the  style  of  mount- 
ing here  recommended,  the  breakage  of  the  Hempel  pipettes  is 
very  slight,  and  the  life  of  the  apparatus  is  much  greater  than 
when  the  pipettes  are  mounted  on  light  wooden  frames,  or  are 
held  in  place  by  clamps  and  corks  as  some  writers  have  advised. 


GAS  ANALYSIS   OVER  WATER 


55 


The  capillary  tube  should  project  from  two  to  three  cm.  above 
the  frame.  A  short  piece  of  rubber  tubing  is  wired  on  the 
free  end  of  the  capillary. 

The  Hempel  Simple  Absorption  Pipette  for  Solid  and 
Liquid  Reagents 

The  only  difference  between  this  and  the  simple  pipette  is 
that  in  place  of  the  bulb  b  there  is  inserted  the  cylindrical  part 


FIG.  35 

A  (Fig.  35),  which  can  be  filled  with  solid  substances  through 
the  neck  N.  This  neck  is  closed  by  a  cork  or  rubber  stopper 
which  is  held  in  place  by  a  wire. 

A  glass  tube  closed  at  the  top,  and  over  which  a  rubber  ring, 
cut  from  a  rubber  tube,  is  drawn,  also  makes  a  good  stopper. 
By  this  arrangement  only  a  narrow  strip  of  rubber  is  exposed 
to  the  action  of  the  reagent. 


56  GAS  ANALYSIS 

Pipettes  of  this  form  are  used  for  the  determination  of  oxygen 
by  means  of  phosphorus  (see  p.  163).  In  such  case  it  is  neces- 
sary to  protect  the  reagent  from  the  action  of  the  light  when 
the  pipette  is  not  in  use,  which  is  done  either  by  covering  the 
pipette  with  a  light  box,  or  by  making  the  cylinder  A  of  brown 
glass.1 

THE  HEMPEL  DOUBLE  ABSORPTION  PIPETTES 

Reagents  that  are  acted  upon  by  oxygen,  i.e.  alkaline  pyro- 
gallol,  cuprous  chloride,  ferrous  salts,  etc.,  cannot  of  course  be 
kept  in  the  above  forms  of  pipette,  since  the  reagent  would 
become  inactive  in  a  short  time  through  contact  with  the  air. 
Hempel  first  sought  to  avoid  this  difficulty  by  protecting  the 
reagent  with  a  layer  of  high-boiling  petroleum,  after  first  con- 
vincing himself  that  the  tension  of  the  petroleum,  resulting 
from  its  solubility  in  the  reagent,  did  not  cause  a  perceptible 
error.  It  was  soon  found,  however,  that  although  such  hydro- 
carbons lessen  decidedly  the  access  of  air,  they  do  not  by  any 
means  form  a  perfect  protection.  Further  experiment  on  this 
subject  led  to  the  construction  of  — 

The  Hempel  Double  Absorption  Pipette  for 
Liquid  Reagents  (Fig.  36) 

This  pipette  permits  the  use  of  the  reagents  in  question  under 
an  easily  movable  atmosphere  that  is  free  from  oxygen,  and 
the  reagent  may  be  kept  completely  saturated  with  those  con- 
stituents of  the  gas  that  it  does  not  strongly  absorb,  which  is 
a  great  advantage.  The  pipette  consists  of  the  large  glass  bulb 
A,  of  about  150  cc.  capacity,  and  three  smaller  bulbs,  B,  C, 
and  Z>,  each  containing  only  100  cc.  They  are  connected  by  the 
bent  tubes  E,  F  and  G,  and  end  in  the  bent  capillary  tube  K. 

The  pipette  is  fastened  to  an  iron  stand  in  the  manner  already 
described  (see  p.  54). 

1  Fritz  Friedrichs,  /.  Am.  Chem.  Soc.,  34  (1912),  1513;  Z.  f.  angew.  Chem.,  25 
(1912),  1905. 


GAS  ANALYSIS   OVER  WATER 


57 


The  pipette  is  prepared  for  use  by  slipping  into  the  rubber 
tubing  at  S  the  tip  of  a  burette  containing  the  absorbing  solution 
and  allowing  this  to  flow  into  the  bulb  A  through  the  capillary 
K.  The  flow  of  the  liquid  through  K  may  be  hastened  by  ap- 
plying gentle  suction  with  the  mouth  upon  a  rubber  tube  at- 
tached to  M.  When  the  contents  of  the  burette  has  been  drawn 
into  A,  air  is  blown  by  the  mouth  through  the  rubber  tubing 
attached  to  M.  The  r-, 

air  in  A  is  forced  out  x*-r\ 

through  the  capillary 
and  the  burette  until 
the  liquid  in  B  falls  to 
the  point  E.  The  stop- 
cock of  the  burette  is 
then  closed,  the  burette 
is  again  filled  with  the 
absorbent  and  the  op- 
eration is  repeated  un- 
til the  bulb  A  and  the 
tube  E  are  full.  If  the 
operation  has  properly 
been  performed  the  ab- 
sorbing liquid  should 
fill  the  capillary  K,  the 
bulb  A,  and  the  con- 
necting tube  E  up  to  the  bulb  B,  and  B  should  be  empty.  The 
burette  is  now  disconnected  from  S,  and  suction  is  applied 
at  M  until  the  absorbent  is  drawn  up  to  the  top  of  the  bulb  B, 
if  the  reagent  does  not  absorb  oxygen.  5  is  then  closed  with 
a  pinchcock,  and  water  is  poured  into  M  until  the  bulb  D 
is  full.  Upon  opening  S  and  gently  blowing  into  M  water  will 
rise  in  C  and  the  reagent  in  A ,  and  if  the  filling  has  properly  been 
performed  the  reagent  will  stand  at  the  top  of  the  capillary  K 
when  the  water  in  the  bulb  C  reaches  to  the  top  of  that  bulb. 

If  the  reagent  absorbs  oxygen  the  solution  should,  after  A 


FIG.  36 


5  8  GAS  ANALYSIS 

has  been  filled  with  it,  be  drawn  up  in  B  before  the  introduction 
of  the  water  only  to  about  two-thirds  of  the  height  of  B,  and 
the  bulb  D  filled  with  water  in  the  manner  already  described. 
Upon  the  absorption  of  the  oxygen  from  the  air  by  the  reagent  in 
the  bulb  C  there  will  remain  between  the  liquids  in  the  bulbs 
B  and  C  the  desired  volume  of  gas,  about  100  cc. 


The  Hempel  Double  Absorption  Pipette  for  Solid  and 
Liquid  Reagents  (Fig.  37) 

The  construction  may  easily  be  understood  from  the  figure. 
To  prepare  this  double  pipette  for  use,  turn  it  upside  down,  in- 
troduce through  the  neck  N  of  the  bulb  A  the  solid  substance 
to  be  employed,  close  the 
neck  with  the  stopper,  and 
wire  the  stopper  in  place. 
Bring  the  pipette  into  an 
upright  position  and  fill  it 
with  liquid  in  the  manner 
described  above. 

While  the  reagent  in  the 
simple  pipette  may  be  con- 
sidered to  be  saturated  with 
gas  only  when  it  is  kept  in 
continual  use,  that  in  the 
double  pipette,  on  the  con- 
trary, remains  saturated  for 
an  exceptionally  long  time, 
since  the  diffusion  must 
take  place  through  the  con- 
fining 100  cc.  of  water  and  through  the  narrow  tube  that  con- 
nects the  bulbs  C  and  D.  The  error  caused  by  this  theoretical 
possibility  may  be  wholly  disregarded  in  using  the  pipette. 

When  the  pipettes  are  not  in  use  the  rubber  tubing  on  the 
capillary  should  be  closed  by  the  insertion  of  a  short  piece  of 


FIG.  37 


GAS   ANALYSIS   OVER   WATER  59 

glass  rod.  A  pinchcock  should  not  be  left  on  this  rubber  tubing, 
since  it  causes  rapid  deterioration  of  the  rubber.  The  open  end 
of  the  single  pipettes  may  be  closed  by  the  insertion  of  a  small 
cork. 

MANIPULATION  OF  THE  HEMPEL  APPARATUS 

If  the  burette  has  been  in  use  clean  it  thoroughly,  and  rinse 
it  well  with  water.  Examine  the  rubber  tubing  attached  to 
the  capillary  of  the  burette  to  see  that  it  is  intact  and  that  the 
wire  ligature  is  in  good  condition.  Make  sure  that  the  pinch- 
cock  closes  the  rubber  tubing  completely.  Open  the  pinchcock 
E,  Fig.  38,  and  slip  it  down  over  the  capillary  tube.  Pour  into 
the  open  end  of  B  water  that  has  been  saturated  with  the  gas 
mixture  that  is  to  be  analyzed  until  A  and  B  are  rather  more 
than  half  full. 

Saturation  of  Confining  Water.  —  A  simple  method  of  satu- 
rating the  water  with  the  gas  is  to  place  the  water  in  a  washing 
flask  and  run  the  gas  through  the  flask  until  the  air  has  been 
displaced,  and  to  then  close  the  exit  tube  and  shake  the  con- 
tents of  the  flask  vigorously. 

Filling  Burette  with  Confining  Liquid.  —  Drive  out  all  air 
from  the  large  rubber  tubing  connecting  A  and  B  by  raising 
and  lowering  the  tubes  alternately,  keeping  the  rubber  tubing 
taut  during  this  operation.  Grasp  the  iron  base  D  in  the  left 
hand  and  raise  it  until  the  water  begins  to  flow  out  of  the  top 
of  the  burette.  Then  close  the  rubber  tube  of  the  burette  with 
the  pinchcock,  setting  the  pinchcock  up  close  to  the  end  of  the 
capillary.  Compress  the  rubber  tubing  at  D  between  the  thumb 
and  fingers  of  the  left  hand  and  pour  out  the  excess  of  water 
that  is  in  B. 

Measurement  of  100  cc.  —  To  measure  off  exactly  100  cc.  of 
the  gas  sample,  insert  into  the  rubber  tube  at  the  top  of  the 
burette  a  capillary  tube  connected  with  the  gasometer  or  pipe 
from  which  the  sample  is  to  be  taken,  after  first  displacing  the 
air  in  this  connecting  capillary  by  the  gas  to  be  examined. 


6o 


GAS  ANALYSIS 


M 


FIG.  38 

Grasp  the  upper  part  of  the  level-tube  B  in  the  left  hand.  Lower 
it  below  A  and  open  the  pinchcock  E  with  the  right  hand. 
Draw  somewhat  more  than  100  cc.  of  gas  into  the  burette.  Close 


GAS  ANALYSIS  OVER  WATER  6 1 

the  pinchcock  E,  place  the  level- tube  on  the  table  and  allow  the 
water  in  the  burette  to  run  down  for  one  minute.1  Disconnect 
the  capillary  tube  from  the  gasometer,  raise  the  level-tube  with 
the  right  hand  until  the  gas  in  the  burette  is  compressed  to  a 
volume  less  than  100  cc.  and  then  close  the  rubber  tubing  at  G 
tightly  by  squeezing  it  close  up  to  the  lower  end  of  the  burette 
between  the  thumb  and  first  finger  of  the  left  hand.  Place  the 
level-tube  on  the  table,  grasp  the  iron  base  of  the  burette  with 
the  right  hand  and  keeping  the  rubber  tubing  at  G  still  tightly 
compressed  raise  the  burette  until  the  meniscus  of  the  water 
in  it  is  on  a  level  with  the  eye.  Then  gradually  release  the  pres- 
sure on  the  rubber  tubing  until  the  water  in  the  burette  falls 
exactly  to  the  100  cc.  mark.  Keeping  the  tubing  still  compressed, 
place  the  burette  on  the  table  and  open  the  stopcock  E  for  a 
moment  to  permit  the  excess  of  gas  to  escape.  The  burette 
should  now  contain  100  cc.  of  the  gas  under  atmospheric  pres- 
sure. To  ascertain  whether  this  is  the  case,  grasp  the  base  of 
the  burette  in  the  right  hand  and  of  the  level-tube  in  the  left 
hand  and  holding  the  burette  perpendicularly  lay  the  level- 
tube  at  an  angle  across  it,  and  bring  the  water  in  the  two  tubes 
to  the  same  level.  If  the  measurement  of  the  sample  has  prop- 
erly been  made  the  water  in  the  burette  will  stand  exactly  at 
the  100  cc.  mark. 

Absorption  of  a  Gas.  —  To  remove  an  absorbable  constit- 
uent of  the  gas  the  burette  and  proper  absorption  pipette  are 
connected  in  the  manner  shown  in  Fig.  38.  Place  the  burette 
and  level-tube  on  the  table,  the  level-tube  B  at  the  left,  bring 
up  near  the  side  of  the  burette  the  wooden  stand  S,  and  place 
on  the  stand  a  pipette  containing  the  proper  absorbent.  Insert 
in  H  the  bent  glass  capillary  tube  F.  These  connecting  capillary 
tubes  are  of  the  same  dimensions  as  the  capillary  tubes  of  the 
burette  and  pipette,  namely,  6  mm.  external  diameter  and  one 
mm.  bore.  The  horizontal  portion  is  about  6  cm. 'long  and  the 
legs  each  about  2.5  cm.  long.  Slip  a  piece  of  rubber  tubing  about 

1  See  p.  68. 


62  GAS  ANALYSIS 

30  cm.  long  over  the  tube  M  of  the  pipette.  Grasp  F  between  the 
thumb  and  fingers  of  the  right  hand,  squeeze  the  rubber  tube  E 
on  the  capillary  of  the  burette  between  the  thumb  and  fingers 
of  the  left  hand,  blow  gently  through  M  until  the  liquid  in  the 
pipette  is  driven  to  the  farther  end  of  the  connecting  capillary 
tube  F  and  then  insert  the  end  of  F  into  the  rubber  tube  on  the 
burette.  If  the  connection  is  properly  made  there  will  be  prac- 
tically no  movement  of  the  reagent  in  the  connecting  capillary 
tube. 

Even  if  a  linear  centimeter  of  air  should  appear  in  the  capil- 
lary, the  error  arising  therefrom  may  be  disregarded,  since 
capillary  tubing  with  a  bore  of  about  one  mm.  contains  only 
about  .01  cc.  in  one  linear  cm.  If,  however,  after  F  has  been 
inserted  in  E,  more  than  a  linear  centimeter  of  air  appears  in  F, 
it  shows  that  the  connection  was  carelessly  made,  and  F  should 
be  slipped  out  of  E  and  the  operation  repeated. 

Certain  reagents  should  never  be  allowed  to  come  into  con- 
tact with  the  rubber  tube  at  H.  In  such  case  the  liquid  is  forced 
upward  in  the  capillary  of  the  pipette  until  it  stands  just  below 
the  iron  of  the  frame.  If  quite  accurate  results  are  desired,  al- 
lowance should  be  made  for  the  very  small  amount  of  air  thus 
left  in  the  connecting  capillary  tubes.  This  may  easily  be  done 
by  measuring  the  length  of  the  capillary  tube  that  is  empty  of 
liquid.  Every  ten  centimeters  of  length  corresponds  to  o.i  cc. 
of  air.  This  correction  is  not  necessary  in  ordinary  technical 
analysis. 

When  the  pipette  and  burette  have  been  connected  in  the 
manner  above  described  the  pinchcock  on  E  is  opened,  the 
level- tube  B  is  slowly  raised  and  the  gas  is  driven  over  into  the 
pipette.  Water  is  allowed  to  flow  into  the  capillary  F  until 
it  reaches  the  point  in  the  bend  of  that  tube  to  which  the  reagent 
had  been  driven  over.  The  pinchcock  at  E  is  then  closed.  This 
manipulation  leaves  the  capillary  tube  of  the  pipette  and  the 
greater  part  of  the  bent  connecting  capillary  tube  filled  with 
the  gas  mixture  under  examination  together  with  such  portion 


GAS  ANALYSIS  OVER  WATER  63 

of  the  reagent  as  adheres  to  the  walls  of  these  capillary  tubes. 
This  adhering  reagent  suffices  to  remove  the  greater  part  of 
the  absorbable  constituent  in  the  gas  mixture  because  a  slender 
column  of  the  gas  stands  in  contact  with  a  comparatively  large 
surface  of  the  reagent,  but  even  if  the  absorbable  constituent 
should  constitute  40  per  cent  of  the  gas  mixture,  and  only  half 
of  this  gas  in  the  capillary  tubes  should  be  absorbed  by  the  re- 
agent on  the  walls,  the  error  thus  caused  would  be  negligible 
in  technical  analysis.  This  is  apparent  when  we  consider  that 
the  total  length  of  the  two  capillary  tubes  is  about  40  cm.  and 
that  the  volume  of  gas  in  these  tubes  is,  consequently,  about 
0.4  cc.  The  volume  of  the  absorbable  constituent  would  then 
amount  to  0.16  cc.  and  if  only  half  of  this  were  absorbed  the 
error  would  be  0.08  cc.  These  figures  illustrate  an  extreme  case. 
If  the  absorbable  constituent  amounted  to  not  more  than  20  per 
cent  of  the  gas  mixture  and  if,  as  may  usually  be  expected, 
80  per  cent  of  it  were  absorbed,  the  error  due  to  incomplete 
removal  of  this  constituent  in  the  capillary  tubes  would  be  less 
than  0.02  cc.  After  the  constituent  that  is  to  be  removed  has 
been  entirely  absorbed,  the  gas  is  drawn  back  into  the  burette. 
This  is  done  by  grasping  the  level-tube  with  the  left  hand  and 
bringing  it  into  such  position  that  the  confining  liquid  in  it 
stands  slightly  lower  than  that  in  the  burette.  The  pinchcock 
E  is  opened,  the  level-tube  is  slowly  lowered  and  the  gas  is 
drawn  back  into  the  burette  until  the  liquid  from  the  pipette 
reaches  the  same  point  in  F  at  which  it  originally  stood.  The 
pinchcock  E  is  now  closed,  the  water  in  the  burette  is  allowed 
to  run  down  for  one  minute,  and  the  gas  volume  in  the  burette 
is  then  read  in  the  manner  above  described. 

It  frequently  happens  that  complete  absorption  of  the  gas 
can  be  accomplished  only  by  shaking  the  pipette  after  the  gas 
has  been  driven  over  into  it.  In  such  case  a  second  pinchcock 
is  placed  on  the  rubber  tube  H,  and  after  the  gas  has  been  trans- 
ferred to  the  pipette,  both  E  and  H  are  closed.  The  frame  of 
the  pipette  is  now  grasped  in  the  right  hand,  the  burette  is 


64  GAS  ANALYSIS 

steadied  with  the  left  hand,  and  the  absorbent  is  brought  into 
intimate  contact  with  the  gas  by  gently  rocking  the  stand  back- 
ward and  forward  on  the  front  edge  of  its  base. 

If  the  reagent  has  no  appreciable  effect  upon  rubber,  much 
time  may  be  saved  in  making  the  connection  between  pipette 
and  burette  by  preparing  the  pipette  in  such  manner  that  it 
will  stand  ready  at  all  times  for  connection  with  the  gas  burette. 
This  is  done  by  placing  a  pinchcock  upon  the  rubber  tube  of  the 
pipette,  inserting  into  this  tube  the  bent  connecting  capillary 
tube,  and  then,  holding  the  pinchcock  open,  driving  the  reagent 
over  nearly  to  the  further  bend  of  this  connecting  capillary  by 
blowing  into  the  large  rubber  tube  attached  to  M.  The  pinch- 
cock is  then  closed.  If  the  operation  has  been  correctly  per- 
formed, the  reagent  should  now  stand  close  to  the  bend  in  the 
connecting  capillary  tube  that  is  nearest  the  burette.  The 
capillary  tube  is  next  inserted  in  the  rubber  tube  of  the  burette 
and  the  absorption  is  made  in  the  manner  above  described. 
After  the  absorption  of  the  gas,  the  reagent  is  drawn  over  nearly 
to  the  further  bend  of  the  connecting  capillary  tube,  and  the 
pinchcock  on  the  pipette  is  then  closed.  This  should  drive  the 
reagent  to  about  the  same  point  in  the  connecting  capillary 
as  that  at  which  it  first  stood.  The  capillary  tube  is  now  with- 
drawn from  the  rubber  tube  that  is  attached  to  the  top  of  the 
burette,  and  the  pipette  is  removed.  The  pipette,  with  the  bent 
capillary  tube  attached  to  it,  now  stands  filled  with  the  reagent 
to  the  further  bend  of  the  connecting  capillary  and  is  ready  for 
immediate  connection  with  the  burette  when  another  determina- 
tion of  the  same  constituent  gas  is  to  be  made. 

The  manipulation  of  the  pipettes  filled  with  solid  absorbents 
is  still  simpler,  for  in  this  case  no  shaking  is  necessary  because 
of  the  large  surface  of  contact  between  the  solid  and  the  gas. 
On  this  account  also  the  apparatus  need  not  be  disconnected. 

The  Hempel  apparatus  for  technical  gas  analysis  possesses 
many  points  of  superiority  over  other  forms  of  apparatus.  It 
is  not  fragile  and  if  a  part  is  broken  it  is  easily  replaced.  It 


GAS  ANALYSIS  OVER  WATER  65 

contains  no  stopcocks.  It  is  easily  cleaned.  Either  water  or 
mercury  may  be  used  as  the  confining  liquid.  When  water  is 
employed,  it  is  easily  saturated  with  the  gas  mixture  under  analy- 
sis. The  pipettes  avoid  waste  of  reagent  and  protect  the  reagents 
from  the  air.  The  removal  of  absorbable  constituents  of  a  gas 
mixture  may  rapidly  and  completely  be  effected. 

Absorbing  Power  of  a  Reagent.  —  If  the  absorbing  power 
of  the  reagent  is  known,  waste  may  be  avoided,  and  with  one 
filling  of  the  pipette  several  hundred  analyses  (the  number 
depending  upon  the  nature  of  the  gases  examined)  may  be 
made,  with  certainty  throughout  as  to  the  efficiency  of  the  ab- 
sorbent. 

To  determine  the  absorbing  power  of  a  reagent,  Hempel 
uses  a  pipette  of  the  form  shown  in  Fig.  39.  The  pipette  is 
filled  with  mercury,  and  then  one  cc.  of  the  solution  of  the  re- 
agent is  drawn  in  through  the  capillary  d.  Mercury  is  allowed 
to  follow  the  solution  so  that  the  reagent  is  inclosed  between 
the  mercury  in  the  pipette  and  the  mercury  standing  in  the 
capillary.  The  pipette  is  connected  by  means  of  rubber  tubing 
and  a  bent  capillary  tube  with  a  Hempel  burette  containing 
the  gas  under  consideration.  The  gas  is  drawn  into  the  pipette 
and  shaken  with  the  reagent  as  long  as  rapid  absorption  takes 
place.  It  is  then  passed  back  into  the  burette  and  measured. 
The  absorbing  power  of  the  reagent  thus  experimentally  de- 
termined is  much  higher  than  could  safely  be  relied  upon  in 
actual  gas  analysis,  and  consequently  under  the  assumption  that 
only  a  fourth  of  the  active  reagent  should  be  used  up  if  there 
is  to  be  no  doubt  as  to  its  absorbing  power,  the  result  in  each 
case  is  divided  by  four  and  the  figure  thus  obtained  is  termed 
the  analytical  absorbing  power  of  the  reagent.  This  figure,  of 
course,  refers  to  the  absorbing  power  of  one  cc.  of  the  reagent. 
To  illustrate,  one  cc.  of  a  33  per  cent  solution  of  potassium 
hydroxide  was  found  to  absorb  readily  160  cc.  of  carbon  dioxide. 
The  analytical  absorbing  power  of  a  solution  of  potassium 
hydroxide  of  the  above  strength  is  consequently  stated  to  be 


66 


GAS  ANALYSIS 


40,  which  means  that  one  cc.  of  the  reagent  may  be  relied  upon 
to  absorb  40  cc.  of  carbon  dioxide  in  gas  analytic  work. 

If  an  accurate  account  is  kept  of  the  amount  of  gas  that  the 

i 


FIG.  39 

reagent  in  a  pipette  has  absorbed,  the  efficiency  of  the  reagent 
still  remaining  in  a  pipette  is  always  known,  and  the  absorbent 
can  be  used  to  the  full  extent  of  its  analytical  absorbing  power 
without  uncertainty  as  to  the  accuracy  of  the  analysis. 


GAS  ANALYSIS  OVER  WATER  67 

Accuracy  of  Analyses  with  the  Hempel  Apparatus.  —  The 

criticism  has  been  urged  against  the  Hempel  apparatus  that  it 
is  cumbersome,  and  that  as  a  consequence  rapid  analytical  work 
cannot  be  performed  with  it.  Those  who  are  familiar  with  the 
manipulation  of  the  various  standard  forms  of  apparatus  for 
technical  gas  analysis  will,  however,  probably  concur  in  the 
statement  that  an  analysis  of  any  of  the  usual  gas  mixtures 
can  be  performed  with  the  Hempel  apparatus  with  as  great 
or  even  greater  speed  than  that  attainable  with  almost  any  other 
device,  and  with  an  accuracy  far  surpassing  that  of  most  other 
technical  methods  and  approximating  that  obtained  over  mer- 
cury. This  is  shown  by  two  partial  analyses  of  illuminating 
gas: 

I.  Technical  II.  Technical  Exact  Analysis  over 

Analysis  Analysis  Mercury 

i .  6  per  cent  i .  5  per  cent          i .  5  per  cent  carbon  dioxide 

3.1       "  2.9       "  3.0       "         heavy  hydrocarbons 

1.4      "  1.6      "  1.4       "         oxygen 

It  should  be  borne  in  mind,  however,  that  with  the  Hempel 
apparatus  for  technical  gas  analysis,  as  with  any  other  form  of 
apparatus,  errors  so  large  that  they  may  entirely  destroy  the 
value  of  the  analysis  will  result  when  the  reagents  and  the 
confining  water  do  not  have  the  temperature  of  the  laboratory 
or  when  there  is  appreciable  change  in  temperature  during  the 
brief  time  necessary  for  the  analysis.  A  rise  of  temperature 
of  only  one  degree  would  cause  an  error  of  0.3  %  in  a  total 
volume  of  100  cc.,  which  makes  it  evident  that  the  analysis 
should  be  made  in  a  laboratory  that  is  of  nearly  constant  tem- 
perature, or,  if  the  work  must  be  done  outside  of  the  laboratory 
under  fluctuating  temperature,  the  burette  should  be  surrounded 
with  a  water  jacket.  The  jacketing  of  the  Hempel  burette  may 
easily  be  effected  by  slipping  down  over  the  burette  an  inverted 
single  bore  rubber  stopper  about  4  cm.  in  diameter,  and  slip- 
ping over  the  burette  and  upon  the  stopper  a  large  glass  tube 
somewhat  shorter  than  the  burette,  holding  the  upper  end  in 


68  GAS  ANALYSIS 

place  by  means  of  a  split  cork.    The  larger  tube  is  then  filled 
with  water. 

Running  Down  of  Confining  Liquid.  —  It  is  also  of  import- 
ance, if  accurate  results  are  desired,  that  the  confining  liquid 
over  which  the  gas  is  measured  be  allowed  to  flow  down  the 
walls  of  the  burette  in  exactly  the  same  manner  and  for  the 
same  length  of  time  after  each  absorption.  If  the  tube  of  the 
Hempel  burette  is  clean,  the  running  down  of  water  is  practically 
complete  in  three  minutes.  If  the  burette  is  allowed  to  stand 
two  minutes  longer  and  the  water  given  five  minutes  in  all 
to  run  down,  the  meniscus  will  stand  from  .02  to  .03  cc. 
higher  than  after  three  minutes,  a  difference  that  is  negligible  in 
technical  gas  analysis  with  water  as  the  confining  liquid.  In 
the  description  of  the  manipulation  of  the  apparatus  on  page  61 
it  was  stated  that  the  water  should  be  allowed  to  run  down  for 
one  minute.  The  results  will  naturally  be  more  accurate  if  the 
three  minute  interval  is  employed,  but  for  technical  analyses 
where  speed  is  a  desideratum  and  great  accuracy  is  not  neces- 
sary, much  time  may  be  saved  by  making  the  readings  only 
one  minute  after  the  gas  has  been  passed  back  into  the  burette. 
The  following  analyses  made  by  Dr.  R.  P.  Anderson  in  the 
Cornell  Laboratory  show  the  variation  in  the  results  when  the 
water  in  the  burette  is  allowed  to  run  down  one,  two,  three  and 
five  minutes. 

Determination    of   Oxygen    with    the    Phosphorus    Pipette 
August  8,   1911 

i  Minute  2  Minutes  3  Minutes  5  Minutes 

I  20 . 6                        20 . 7                        20 . 8  20 . 8 

II  20 . 6                        20 . 7                        20 . 8  20 . 8 

III  20.6                       20.7                       20.8  20.8 

In  apparatus  in  which  gas  volumes  are  read  over  liquids  other 
than  water  or  mercury,  such  as  solutions  of  fixed  alkalies, 
cuprous  chloride,  alkaline  pyrogallol,  and  the  like,  the  running 
down  of  the  liquid  takes  place  slowly,  and  an  error  in  measure- 


GAS  ANALYSIS  OVER  WATER 


69 


merit  of  one  cubic  centimeter  or  more  may  result  if  the  reading 
is  not  made  under  exactly  the  same  conditions  in  all  cases. 
While  distilled  water  will  run  down  completely  in  a  Hempel 
burette  in  five  minutes,  a  five  per  cent  solution  of  sodium  hy- 
droxide requires  ten  minutes  and  concentrated  sulphuric  acid 


FIG.  40 

from  fifteen  to  twenty  minutes.  If  in  an  analysis  of  a  gas 
mixture  the  residual  gas  volumes  are  read  first  over  one  liquid 
and  then  over  another,  it  is  apparent  that  rapid  and  at  the  same 
time  accurate  work  is  almost  if  not  quite  impossible. 

Portable  Hempel  Apparatus.  —  It  must  be  conceded  that  the 
Hempel  apparatus  is  not  easy  to  carry  about,  but  for  the  analysis 


yd  GAS  ANALYSIS 

of  rather  simple  gas  mixtures  this  objection  is  obviated  by  the 
portable  Hempel  apparatus  devised  by  the  present  writer  and 
shown  in  Fig.  40.  The  burette  A  has  a  capacity  of  50  cc.  and 
is  calibrated  in  one-fifth  cc.  It  is  set  in  a  square  iron  base  that 
is  grooved  on  two  sides  and  slips  over  the  wooden  guides  shown 
in  the  drawing.  The  level-tube  B  is  similarly  mounted  and 
lies  on  the  bottom  of  the  case  opposite  the  burette.  The  case 
contains  three  Hempel  gas  pipettes,  one,  E,  a  simple  pi- 
pette for  solid  reagents,  and  two,  C  and  D,  double  pipettes 
for  liquid  reagents.  These  pipettes  are  mounted  on  wooden 
frames  to  lessen  the  weight  of  the  apparatus.  The  ap- 
paratus may  be  obtained  with  pipettes  of  different  forms  than 
those  here  given  if  the  analyst  should  so  desire.  The 
drawer  F  contains  small  accessories  such  as  rubber  tubing 
for  connections,  and  the  bent  capillary  tubes  for  joining  the 
burette  with  the  pipettes.  The  front  and  the  back  of  the  case 
are  fitted  with  sliding  covers,  and  the  top  is  provided  with  a 
metal  handle.  The  apparatus  is  quite  compact,  the  dimensions 
of  the  outer  case  being  20.5  cm.  long,  n  cm.  high,  and  8  cm. 
wide.  The  total  weight  of  the  apparatus  when  the  pipettes 
are  not  filled  is  6.8  kilograms. 

It  was  formerly  necessary  to  analyze  gas  mixtures  containing 
carbon  dioxide  at  the  place  where  the  sample  is  taken,  because 
of  the  difficulty  of  obtaining  a  proper  average  sample  of  a  gas 
mixture  containing  this  ingredient  and  of  transporting  it  to  the 
laboratory  without  change  in  its  composition.  The  Huntly 
sample  tube  described  on  p.  5  appears  to  remove  this  diffi- 
culty. 

THE  MODIFIED  WINKLER  GAS  BURETTE    (Fig.  41) 

This  gas  burette  is  of  use  in  the  determination,  directly  in 
the  burette,  of  gases  that  are  readily  soluble  in  water,  such  as 
ammonia  or  hydrogen  chloride.  Yet  when  a  gas  mixture  con- 
tains gases  that  are  easily  soluble  in  water,  it  is  generally 
preferable  to  pass  a  large  volume  of  the  gas  mixture  through  a 


GAS  ANALYSIS  OVER  WATER 


suitable  absorbent,  and  to  then 
determine  the  absorbed  gas  by 
titration. 

The  Winkler  burette  consists 
of  the  level-tube  a  and  the 
measuring  tube  b  connected  by 
a  rubber  tube  about  120  cm. 
long  and  fastened  into  iron  feet. 
b  is  a  glass  tube  of  about  100  cc. 
capacity,  provided  with  the 
three-way  cock  c  and  the  sim- 
ple glass  stopcock  d.  The  space 
between  the  two  stopcocks  is 
divided  into  exactly  100  equal 
parts,  and  each  part  into  fifths. 
The  capillary  e  has  the  same  di- 
mensions as  that  on  the  Hempel 
burette.  Instead  of  the  glass 
stopcock  d  a  rubber  tube  and 
pinchcock  may  be  used  as  with 
the  simple  burette. 

Manipulation  of  the  Wink- 
ler Burette.  —  Before  filling  the 
burette  with  the  easily  soluble 
gases,  the  tube  b  is  first  dried  by 
rinsing  it  out  with  a  few  cubic 
centimeters  of  absolute  alcohol 
and  then  with  ether,  the  latter 
being  driven  out  by  aspirating 
through  the  tube  the  gas  to  be 
analyzed.  To  do  this,  join  the 
end  e  of  the  burette  by  means 
of  a  rubber  tube,  or  better  a 
glass  tube,  to  the  vessel  contain- 
ing the  gas  and  bring  the  three- 


FIG.  41 


72  GAS  ANALYSIS 

way  cock  into  such  a  position  that  its  longitudinal  opening 
communicates  with  the  inside  of  the  burette.  Connect  the  cock 
with  the  aspirator.  After  the  gas  has  been  drawn  through  for 
a  time,  close  the  upper  stopcock  and  turn  the  lower  stopcock 
through  an  angle  of  180°.  Place  upon  the  tail  of  the  lower 
(three-way)  stopcock  a  short  piece  of  rubber  tubing  and  close 
this  with  a  pinchcock.  The  gas,  if  under  pressure,  is  brought 
to  atmospheric  pressure  by  momentarily  opening  the  upper 
stopcock.  The  remainder  of  the  apparatus  is  now  filled  with 
water  run  in  through  the  three-way  cock,  which  is  so  turned 
that  it  communicates  with  the  rubber  tube.  The  water  must 
previously  be  saturated  with  those  constituents  of  the  gas 
mixture  which  are  slightly  soluble  in  water.  The  easily  soluble 
gas  in  the  mixture  is  then  absorbed  by  turning  c  into  such 
position  that  a  and  b  are  connecting,  allowing  some  water 
from  a  to  rise  in  £,  closing  c  and,  with  b  held  in  a  horizontal 
position,  running  water  backward  and  forward  to  promote 
the  absorption  of  the  gas.  b  is  then  placed  in  an  upright 
position,  c  is  opened  and  the  residual  gas  volume  is  read. 
c  is  then  closed  and  the  gas  in  b  is  shaken  again  with  the 
water,  and  after  opening  c  the  volume  is  again  read.  This  is 
continued  until  no  further  diminution  of  the  gas  volume  in  b 
takes  place.  The  constituents  that  are  only  slightly  soluble 
in  water  are  determined  by  absorption  in  the  Hempel  pipette 
in  the  usual  manner. 

THE  HONIGMANN  GAS  BURETTE 

The  Honigmann  gas  burette  is  suited  only  to  the  rapid  and 
approximate  determination  of  carbon  dioxide  in  gas  mixtures 
that  contain  fairly  high  percentages  of  this  constituent. 

The  burette  A  (Fig.  42)  contains  100  cc.  divided  into  f  cc., 
the  zero  point  being  at  the  lower  end  of  the  burette.  At  the 
top  it  is  closed  by  a  glass  stopcock  and  the  lower  end  below 
the  graduation  is  drawn  out  to  smaller  diameter  to  permit 
of  a  piece  of  rubber  tubing  being  easily  slipped  over  it.  The 


GAS  ANALYSIS   OVER  WATER 


73 


absorbing  liquid,  potassium  hydroxide,  is  placed  in  a  glass  cylin- 
der c,  which  should  be  tall  enough  to  allow  the  burette  to  be 
lowered  to  any  desired  point  into  the  liquid. 
Manipulation  of  the  Honigmann 
Burette.  —  In  making  a  determination, 
the  burette  is  first  thoroughly  cleaned 
with  water,  and  the  gas  to  be  analyzed  is 
then  passed  through  it  until  all  air  in  the 
burette  has  been  displaced.  Stopcock  a 
is  now  closed  and  the  rubber  tube  is  im- 
mersed in  a  solution  of  potassium  hy- 
droxide in  the  manner  shown  in  the  fig- 
ure. The  solution  of  potassium  hydroxide 
contains  one  part  of  commercial  potas- 
sium hydroxide  dissolved  in  two  parts  of 
wrater.  The  burette  is  lowered  into  this 
solution  until  the  liquid  stands  exactly  at 
the  zero  point.  The  stopcock  a  is  then 
carefully  opened  until  the  liquid  inside  the 
burette  rises  to  the  same  mark,  and  it  is 
then  closed.  The  tube  now  contains  100 
cc.  of  the  gas  at  atmospheric  pressure. 
The  absorption  of  the  carbon  dioxide  is 
effected  by  grasping  the  burette  between 
the  thumb  and  fingers  in  the  manner 
shown  in  the  figure,  and  turning  it  down- 
ward so  that  the  caustic  potash  will  flow 
along  the  walls  of  the  burette.  During 
this  operation  the  open  end  of  the  rubber 
tube  must,  of  course,  remain  below  the 
surface  of  the  solution  in  the  cylinder. 
After  all  the  carbon  dioxide  has  been  absorbed,  the  burette  is 
again  brought  to  a  perpendicular  position  and  is  lowered  into  the 
liquid  in  the  cylinder  until  the  liquid  surfaces  on  the  inside  and 
outside  of  the  burette  stand  at  the  same  height.  The  reading 


FIG.  42 


74  GAS  ANALYSIS 

is  now  taken,  and  the  result  gives  directly  the  percentage  amount 
of  carbon  dioxide  present  in  the  original  gas  mixture. 


THE   BUNTE   GAS   BURETTE 

The  Bunte  burette  may  be  used  for  the  approximate  determi- 
nation of  carbon  dioxide  and  oxygen. 

The  burette  A  (Fig.  43)  is  closed  at  the  top  by  the  three-way 
stopcock  C,  and  above  this  there  is  the  tube  Z>,  which  is  pro- 
vided with  a  mark  about  5  cm.  above  the  stopcock.  The  lower 
end  of  the  burette  is  closed  by  a  simple  glass  stopcock,  and  is 
connected  with  the  level-bottle  B  by  a  long  piece  of  rubber 
tubing.  A  pinchcock  is  placed  upon  this  rubber  tube  a  short 
distance  below  the  end  of  the  burette.  Inasmuch  as  all  of  the 
readings  with  this  burette  will  probably  lie  between  the  zero 
point  and  the  50  cc.  mark,  the  instrument  is  made  shorter,  and 
consequently  easier  to  handle,  by  widening  the  upper  portion. 
The  horizontal  opening  of  the  stopcock  C  is  closed  by  a  piece  of 
rubber  tubing  and  a  pinchcock.  The  burette  and  level-bottle 
are  supported  on  an  iron  stand  of  the  form  shown  in  the  figure, 
the  burette  being  held  in  a  spring  clamp  which  permits  of  its 
easy  removal.  The  calibration  of  the  burette  runs  from  the 
zero  point,  which  is  near  the  lower  end,  up  to  100  cc.  at  the 
upper  stopcock.  The  calibration  is  carried  on  below  the  zero 
point  for  10  cc.  There  must  also  be  provided  a  thick  walled 
glass  bottle  5*  supplied  with  a  one-hole  rubber  stopper  carrying 
a  short  piece  of  glass  tubing  which  is  closed  by  a  piece  of  rubber 
tubing  and  a  screw  pinchcock.  A  piece  of  glass  tubing  bent 
in  the  shape  0  is  also  necessary  for  running  water  into  D. 

Manipulation  of  the  Bunte  Burette.  —  Fill  the  level-bottle 
B  with  water,  connect  the  rubber  tube  with  the  burette  in 
the  manner  shown  in  the  figure,  open  the  pinchcock  H  and 
the  two  stopcocks  of  the  burette,  and  allow  water  to  rise 
in  the  burette  until  D  is  partially  filled.  Close  G  and  H.  Now 
turn  the  stopcock  C  until  D  communicates  with  F,  and  open 


GAS  ANALYSIS  OVER  WATER 


75 


the  pinchcock  on  F  until  the  bore  of  the  stopcock  and  the  rub- 
ber tube  are  filled  with  water.  Then  close  the  pinchcock.  Slip 
the  pinchcock  H  up  to  the  lower  end  of  the  burette.  Close  it, 
and  remove  the  long  rub- 
ber  tube  from  the  bu-  D 

rette.  Place  under  the 
burette  a  beaker  to  catch 
the  water  which  runs  out. 
Connect  F  with  the  res- 
ervoir containing  the 
gas  to  be  analyzed,  and 
open  the  pinchcock  on  F 
and  the  lower  glass  stop- 
cock of  the  burette.  The 
water  in  the  burette  will 
now  flow  out,  and  the  gas 
will  be  drawn  over  into 
the  tube.  Draw  into  the 
burette  rather  more  than 
100  cc.  of  gas. 

The  gas  in  the  burette 
is  always  read  at  the 
pressure  of  the  atmos- 
phere plus  the  pressure 
of  the  column  of  water 
standing  in  D  up  to  the 
mark.  For  convenience 
in  calculating  results  it 
is  desirable  that  the  orig- 
inal volume  be  exactly 
100  cc.  at  this  pressure. 
To  measure  off  this  exact 
volume  close  the  stop- 
cock C,  open  the  pinch- 
cock H  until  the  long 


FIG.  43 


76  GAS  ANALYSIS 

rubber  tube  is  filled  with  water,  and  then  slip  this  carefully 
over  the  lower  end  of  the  burette,  after  first  making  sure 
that  there  are  no  bubbles  of  gas  in  the  tip  of  the  burette 
below  the  stopcock.  Now  open  H  and  G,  and  allow  water  to 
rise  nearly  to  the  zero  point.  Close  G,  and  then  turn  C,  so  that 
A  communicates  with  D.  Since  the  gas  in  the  burette  is  under 
slight  pressure,  bubbles  will  escape  upward  through  the  water  in 
D.  Bring  the  water  in  D  exactly  to  the  mark,  and  then  by 
carefully  opening  G  allow  the  water  in  the  burette  to  rise 
until  it  stands  exactly  at  zero.  There  is  now  in  the  burette 
100  cc.  of  gas  under  the  pressure  of  the  atmosphere  plus 
the  column  of  water  in  D.  Close  C,  and  proceed  to  the  ab- 
sorption of  the  constituent  of  the  gas  mixture  that  is  to  be 
determined. 

This  absorption  is  brought  about  by  introducing  a  liquid  ab- 
sorbent into  the  burette  through  the  lower  end.  Since  these 
absorbents  for  the  various  gases  are  usually  concentrated  solu- 
tions, it  is  undesirable  to  allow  the  absorbent  to  be  diluted  by 
the  water  still  remaining  in  the  burette  between  G  and  the 
zero  point.  This  water  is  therefore  first  removed  with  aid  of 
the  suction  bottle  S.  This  bottle  is  connected  by  means  of  the 
rubber 'tube  at  its  top  with  a  water  suction  pump,  and  is  ex- 
hausted of  air.  The  screw  pinchcock  is  then  closed,  the  long 
rubber  tube  is  slipped  off  from  the  lower  end  of  the  burette, 
and  the  rubber  tube  of  S  is  slipped  over  the  burette  tip.  The 
screw  pinchcock  on  S  is  now  opened,  G  is  then  carefully  turned, 
and  the  water  in  the  burette  is  slowly  drawn  off  until  it  has 
fallen  to  a  point  just  above  G.  G  is  then  closed,  the  pinchcock 
of  5  is  closed,  and  the  suction  bottle  is  detached.  This  operation 
serves  also  to  bring  the  pressure  of  the  gas  in  the  burette  below 
that  of  the  atmosphere,  and  thus  renders  it  possible  to  intro- 
duce the  reagent  through  the  lower  end  of  the  burette.  The  re- 
agent to  be  introduced  into  the  burette  is  now  poured  into  a 
small  evaporating  dish,  and  this  dish  is  brought  up  under  the  tip 
of  the  burette;  G  is  carefully  opened,  and  the  liquid  at  once  rises 


GAS  ANALYSIS   OVER  WATER  77 

in  the  burette.  When  no  more  will  enter,  close  G,  remove  the 
dish,  grasp  the  burette  with  the  thumb  and  the  first  two  fingers 
of  the  left  hand  at  the  stopcock  C,  and  open  the  spring  clamp 
with  the  right  hand.  Place  the  first  and  second  fingers  of  the 
right  hand  below  the  stopcock  G,  pour  out  the  water  in  Z>,  and 
tip  the  burette  backwards  and  forwards  so  that  the  absorbing 
liquid  will  flow  along  its  entire  length.  Place  it  again  in  the 
clamp,  bring  the  dish  of  the  absorbent  under  the  tip,  and  allow 
more  liquid  to  enter  if  it  will,  repeating  the  tilting  of  the  burette 
in  the  manner  just  described.  When  the  absorbent  will  rise 
no  farther  in  the  burette,  that  is,  when  the  absorption  of  the 
gas  is  completed,  place  the  burette  in  the  clamp  in  such  a  posi- 
tion that  its  upper  end  is  below  the  level-bottle  B,  put  a  beaker 
under  G,  and  insert  in  the  end  of  the  rubber  tube  of  B  the 
fl -shaped  glass  tube  already  mentioned.  Hook  this  tube  over 
the  edge  of  D.  Open  the  pinchcock  H  so  that  water  will  flow  into 
D,  then  open  C,  and  lastly  open  G.  Water  will  now  flow  through 
the  burette  and  wash  out  the  absorbent,  and  yet  no  gas  will 
escape  during  the  operation.  When  the  absorbent  has  been 
removed  in  this  manner,  close  G,  shut  off  the  supply  of  water 
from  B,  and  then  carefully  open  G  until  the  water  in  D  falls 
just  to  the  mark.  Read  the  volume  of  gas  now 'remaining  in 
the  burette.  The  difference  between  this  volume  and  the  origi- 
nal volume  of  100  cc.  will  give  the  per  cent  of  gas  which  has 
been  absorbed.  The  same  procedure  is  followed  in  the  determi- 
nation of  a  second  constituent  in  the  same  sample. 

Throughout  the  entire  operation  be  sure  not  to  touch  with 
the  hand  any  part  of  the  burette  except  the  two  stopcocks, 
since  otherwise  the  heat  of  the  hand  would  expand  the  gas  in 
the  burette  and  cause  some  of  it  to  escape  through  the  open 
stopcock  C. 

Determinations  with  the  Bunte  burette  cannot  be  accurate, 
since  the  gas  in  the  burette  is  brought  into  contact  with  large 
volumes  of  water  that  is  unsaturated  with  the  gas  mixture, 
and  which  will  therefore  absorb  some  of  the  gas  of  the  sam- 


78  GAS  ANALYSIS 

pie.1  The  method  is  also  wasteful  of  reagent,  since  the  reagent 
which  has  once  been  employed  cannot  be  used  over  again  be- 
cause of  its  dilution  by  the  wash  water. 

THE  ORSAT  APPARATUS 

In  the  analysis  of  commercial  grades  of  sodium  carbonate 
there  early  arose  a  demand  for  a  rapid  and  convenient  method 
for  the  determination  of  carbon  dioxide,  which  was  met  in  1868 
by  the  apparatus  designed  by  Schlosing  and  Rolland.2  In  1874 
Orsat  patented  a  device3  that  was  based  directly  upon  the 
principle  of  the  apparatus  of  Schlosing  and  Rolland,  and  that 
attracted  considerable  attention  at  the  time  and  rapidly  came 
into  general  use.  Because  of  its  compactness  and  ease  of  manip- 
ulation the  Orsat  apparatus  has  been  and  still  is  very  generally 
employed  by  gas  analysts.  In  its  original  form,  however,  and 
even  in  some  of  the  later  modifications  it  possesses  certain 
inherent  faults,  and  the  unsatisfactory  character  of  the  analyti- 
cal results  that  are  obtainable  with  the  various  forms  is  evi- 
denced by  the  large  number  of  changes  in  its  construction 
that  are  constantly  being  brought  forward  in  chemical  journals. 
The  chief  objection  to  the  apparatus  is  the  incompleteness  of 
the  absorption  of  such  gases  as  oxygen  and  carbon  monoxide. 
The  researches  of  Gautier  and  Clausmann,  Bendemann,  Hankus, 
Hempel,  Nowicki,  Hahn,  Dennis  and  Edgar  and  others  have 
demonstrated  that  the  complete  removal  of  oxygen  by  alkaline 
pyrogallol  and  of  carbon  monoxide  by  cuprous  chloride  can  be 
effected  only  when  the  absorbent  and  the  gas  are  shaken  to- 
gether, or  when  the  gas  is,  in  some  manner,  brought  into  pro- 
longed and  intimate  contact  with  the  absorbent.  With  most 

1  The  manner  of  manipulation  of  the  Bunte  burette  described  by  Haber  in  the 
Journal  fur  Gasbeleuchtung,  39  (1896),  802,  lessens  the  errors  due  to  the  absorption 
of  the  gases  by  the  wash  water,  but  is  probably  too  inconvenient  to  be  generally 
followed.    If  the  burette  is  used  in  the  customary  manner,  it  does  not  give  accurate 
results. 

2  Annales  de  chimie  et  de  physique,  4  serie,  14  (1868),  55, 

3  Chem.  News,  29  (1874),  177. 


GAS  ANALYSIS  OVER   WATER  79 

of  the  suggested  forms  of  the  Orsat  absorption  pipette,  the 
removal  of  oxygen  and  carbon  monoxide  is  quite  incomplete 
unless  the  gas  is  allowed  to  stand  in  contact  with  the  absorbent 
for  a  very  considerable  length  of  time,  or  is  passed  back  and 
forth  many  times  between  the  burette  and  pipette.  Failure  to 
recognize  this  inadequacy  of  the  apparatus  frequently  results 
in  the  incomplete  removal  of  oxygen,  and,  as  a  consequence,  a 
decrease  in  volume  is  observed  when  the  gas  mixture  is  next 
passed  into  the  cuprous  chloride  pipette.  In  very  many  cases 
the  analyst  has  in  this  manner  been  led  into  reporting  carbon 
monoxide  in  a  gas  mixture,  such  as  flue  gas,  when  in  fact  no 
carbon  monoxide  is  present,  the  decrease  in  volume  being  due 
solely  to  the  absorption,  by  cuprous  chloride,  of  oxygen  that 
still  remains  in  the  gas  mixture. 

In  recent  years  several  interesting  and  some  valuable  sug- 
gestions for  increasing  the  completeness  and  rapidity  of  ab- 
sorption in  the  Orsat  apparatus  have  appeared  in  chemical 
journals.  Bendemann  proposes  *  that  two  pipettes  be  used  for 
the  absorption  of  oxygen  by  alkaline  pyrogallol  and  two  for  the 
removal  of  carbon  monoxide  by  cuprous  chloride.  This  would 
undoubtedly  lessen  the  errors  of  the  determinations  but  would 
hardly  remove  them  entirely.  More  worthy  of  consideration 
are  the  proposed  modifications  of  the  form  of  the  absorption 
pipette  to  bring  gas  and  liquid  into  intimate  contact.  Most 
of  these  are  based  upon  the  construction  described  in  1899  by 
E.  Hankus  2  and  shown  in  Fig.  44.  The  gas  enters  the  pipette 
through  A,  passes  downward  through  the  capillary  and,  by 
impinging  on  the  plate  £,  is  broken  up  into  minute  bubbles 
which  then  pass  upward  through  the  absorbing  liquid.  The 
gas  is  brought  back  into  the  burette  by  turning  the  stopcock 
through  an  angle  of  180°  and  lowering  the  level-bottle  of  the 
burette. 

In  1911  the  Chemists'  Committee  of  the  United  States  Steel 

1  Jour.f.  Gasbeleuchtung,  49  (1906),  853. 

20sterr.  Chem.  Ztg.,  47  (1899),  81;  /.  Gasbeleuchtung,  49  (1906),  367. 


So 


GAS  ANALYSIS 


Corporation  described  1  an  absorption  pipette  (Fig.  45)  that 
is  quite  similar  to  the  form  proposed  twelve  years  earlier  by 
Hankus,  but  is  slightly  less  efficient  than  the  Hankus  pipette 
(see  results  below)  since  it  permits  the  gas  to  escape  freely  in 
large  bubbles  from  the  lower  end  of  the  capillary  tube. 

The  pipette  devised  by  Nowicki 2  and  improved  by  Heinz  3 
(Fig.  46)  yields  more  complete  absorption  than  that  of  Hankus. 

A 


\ 


FIG.  44 


FIG.  45 


FIG.  46 


The  gas  passes  downward  through  the  straight  capillary  tube  A 
and  then  rises  in  small  bubbles  through  the  spiral  tube  5  which 
insures  long  and  thorough  contact  between  the  gas  and  absor- 
bent. A  short  tube  D  is  attached  to  the  lower  end  of  the  spiral, 
and  fresh  absorbing  liquid  is  drawn  upward  through  this  open- 

1  Met.  and  Ghent.  Eng.,  9  (191 1),  303. 

2  Osterr.  Zeit.  f.  Berg.-Hiitt.,  53  (1905),  337. 

3  /.  Gasbeletichtung,  49  (1906),  367. 


GAS  ANALYSIS  OVER   WATER 


81 


ing  when  the  gas  bubbles  rise  through  the  spiral.  Experience 
has  shown,  however,  that  when  this  form  of  absorption  pipette 
is  used  for  the  determination  of  oxygen  with  alkaline  pyrogallol 
the  gas  is  frequently  trapped  in  the  spiral.  Moreover,  the 
pipette  is  so  fragile  that  it  is  often  broken  in  transportation, 
which  renders  it  unsuitable  for  use  in  a  portable  apparatus. 

The  very  rapid  and  complete  absorption  of  gases  that  upon 
experiment  was  found  to  be  obtainable  with  the  Friedrichs 
gas  washing  bottle 1  led  the 
author  to  employ  the  same  prin- 
ciple in  the  construction  of  an 
absorption  pipette  for  the  Orsat 
apparatus,  the  form  of  pipette 
that  was  finally  adopted  being 
that  shown  in  Fig.  47.  The 
gas  mixture  enters  the  pipette 
through  the  capillary  A  (the 
stopcock  being  in  position  I), 
and,  passing  downward  through 
the  capillary,  escapes  at  B. 
It  then  rises  and  in  so  doing 
follows  the  spiral  S.  The  rising 
gas  carries  some  of  the  absorb- 
ing liquid  with  it,  and  this  liquid 
then  flows  down  on  the  inside  of 
the  cylinder  C  and  mixes  with 
the  main  body  of  the  absorbent 
again  at  D.  After  the  gas  has 
risen  through  the  spiral  and  has 

collected  in  the  space  F,  the  stopcock  is  turned  through  180° 
to  position  II  and  the  gas  is  then  drawn  back  into  the  burette. 

An  experimental  comparison  of  the  different  forms  of  Orsat 
pipette  here  illustrated  has  been  made  by  Mr.  F.  H.  Rhodes. 
In  the  first  series  of  comparative  determinations  oxygen  in 

1 Z.  anal.  Chem.,  50  (1911),  175. 


»— s 


FIG.  47 


82 


GAS  ANALYSIS 


atmospheric  air  was  absorbed  by  means  of  an  alkaline  solution 
of  pyrogallol.  (See  p.  160).  One  hundred  cc.  of  air  was  measured 
off  in  a  Hempel  burette,  and  this  was  then  connected  with  the 
pipette  under  examination,  and  the  gas  sample  was  passed  back 
and  forth  between  the  absorption  pipette  and  the  burette  until 
all  of  the  oxygen  in  the  sample  had  been  absorbed.  The  air 
was  passed  into  the  several  pipettes  at  a  uniform  speed.  The 
absorption  pipettes  that  were  tested  were 

(a)  the  usual  form  of  Orsat  pipette,  which  is  filled  with  glass 
tubes  to  increase  the  absorbing  surface; 

(b)  the  Hankus  pipette  (Fig.  44) ; 

(c)  the  absorption  pipette  recommended  by  the  Chemists' 
Committee  of  the  United  States  Steel  Corporation  (Fig.  45) ; 

(d)  the  Nowicki-Heinz  spiral  absorption  pipette  (Fig.  46) ;  and 

(e)  the  new  form  of  pipette  here  described  (Fig.  47). 


TABLE  I 

The  sample  of  air  was  passed  over  into  each  absorption  pi- 
pette in  one  minute.  It  was  then  immediately  drawn  back  into 
the  burette  and  again  passed  into  the  absorption  pipette  at 
the  same  speed  as  before.  This  was  continued  until  all  of  the 
oxygen  was  absorbed.  The  results  given  in  the  tables  are  the 
averages  of  numerous  determinations. 


Time 
(Minutes) 

(a)  Orsat 
Usual 
Form 

(b)  Hankus 
Pipette 

(c)  U.  S. 
Steel 
Committee 

(d)  Nowicki- 
Heinz 
Pipette 

(e)  Pipette 
New 
Form 

I 

8.0 

II  .  2 

9.0 

20.  6 

18.6 

2 

13-3 

I6.S 

14.2 

20.8 

20.4 

3 

16.7 

19.  1 

17.2 

20.9 

20.9 

4 

18.7 

20.  1 

18.8 

5 

19-5 

20.5 

19.8 

6 

20.2 

20.7 

2O.  2 

7 

2O.4 

20.8 

20.6 

8 

20.8 

20.9 

2O.9 

9 

2O-9 

GAS  ANALYSIS  OVER  WATER 


TABLE  II 

In  the  analyses  here  tabulated,  the  sample  of  air  was  first 
passed  into  each  pipette  in  two  minutes,  that  is,  at  half  the 
earlier  speed.  It  was  then  immediately  drawn  back  into  the 
burette  and  passed  a  second  time  into  the  pipette  in  one 
minute. 


Time 
(Minutes) 

(a)  Orsat 
Usual 
Form 

(b)  Hankus 
Pipette 

(c)  U.  S. 
Steel 
Committee 

(d)  Nowicki- 
Heinz 
Pipette 

(e)  Pipette 
New 
Form 

2 

10.3 

15-6 

12.3 

20.7 

20.  6 

i  minute  more 

17.2 

18.3 

17.2 

20.Q 

20.Q 

The  above  results  render  it  evident  that  the  complete  ab- 
sorption of  oxygen  from  air  can  be  effected  with  the  first  three 
forms  of  pipette  only  by  repeated  passage  of  the  gas  sample 
into  the  pipette  and  back  into  the  burette.  The  Nowicki- 
Heinz  pipette  and  the  spiral  pipette  here  proposed  seem  to  be 
of  nearly  equal  efficiency,  but  the  former  is  open  to  the  objec- 
tions already  noted. 

To  ascertain  the  efficiency  of  the  new  spiral  pipette  in  the 
absorption  of  carbon  monoxide,  mixtures  of  this  gas  with  known 
amounts  of  air  were  prepared;  oxygen  was  determined  in  one 
spiral  pipette  by  absorption  with  an  alkaline  solution  of  pyrogal- 
lol  and  carbon  monoxide  in  a  second  spiral  pipette  by  absorption 
with  an  ammoniacal  solution  of  cuprous  chloride.  In  the  ab- 
sorption of  oxygen  the  gas  mixture  was  passed  into  the  pipette 
in  two  minutes,  was  drawn  back  and  then  passed  in  a  second 
time  in  one  minute.  In  the  absorption  of  carbon  monoxide  the 
same  time  intervals  were  found  to  give  complete  absorption 
of  the  gas  unless  the  amount  of  carbon  monoxide  exceeded 
25  per  cent.  In  such  case  it  was  found  necessary  to  pass  the 
gas  mixture  three  times  into  the  pipette,  the  first  time  in  two 
minutes,  and  the  second  and  third  times  in  one  minute  each. 
The  results  were  as  follows: 


84  GAS  ANALYSIS 


II  in 


(Taken  17.7  16.2  13.2 

I  Found  17.8  16.3  13.2 

.,      (Taken  15.8  22.9  37.3 

Carbonmonox.de  ^  _g  • 


It  thus  appears  that  with  this  form  of  absorption  pipette 
both  oxygen  and  carbon  monoxide  can  be  removed  as  com- 
pletely and  as  rapidly  as  is  possible  with  the  Hempel  absorp- 
tion pipette  in  which  the  gas  and  absorbent  are  shaken  together. 

A  further  error  in  analyses  made  with  the  usual  forms  of 
the  Orsat  apparatus  results  from  the  incorrect  positions  of 
the  measuring  burette.1  After  the  removal  of  the  absorbable 
constituents  of  the  gas  mixture  the  capillary  tube  that  con- 
nects the  burette  with  the  pipettes  remains  filled  with  the  com- 
bustible residue;  consequently,  when  a  portion  of  this  residue 
is  measured  off  in  the  burette  and  is  passed  to  the  combustion 
apparatus  through  the  capillary  tube  above  the  pipettes,  it 
will  carry  with  it  the  combustible  gas  remaining  in  that  capil- 
lary. This  difficulty  may  be  avoided  by  filling  the  connecting 
capillary  with  the  confining  liquid  (water)  in  the  manner  sug- 
gested by  Pfeifer,2  or  more  simply  by  placing  the  burette  be- 
tween the  absorption  pipettes  and  the  combustion  apparatus  in 
the  manner  recommended  by  Hahn.3  Since  the  Orsat  apparatus 
is  chiefly  employed  for  the  determination  by  absorption  in  liquid 
reagents  of  carbon  dioxide,  oxygen,  and  carbon  monoxide,  it 
is,  in  the  opinion  of  the  writer,  preferable  to  limit  the  apparatus 
to  the  determination  of  these  three  gases  and  to  construct  it  in 
such  manner  as  to  render  it  easily  possible  to  connect  the  bur- 
ette, when  so  desired,  with  suitable  special  apparatus  for  the 
determination  of  hydrogen  and  hydrocarbons.  The  apparatus 

1  See  Hahn,  Zeit.  d.  Vereins  deutscher  Ingenieure,  1906;  /.  Gasbeleuchtung,  49 
(1906),  367. 

2/./.  Gasbeleuchtung,  51  (1908),  523. 
3  Loc.  cit. 


GAS  ANALYSIS  OVER  WATER  85 

is  thus  rendered  smaller,  more  easily  portable,  and  less  fragile, 
and  the  combustion  results,  with  proper  apparatus,  will  usually 
be  much  more  accurate  than  with  the  imperfect  devices  con- 
tained in  the  many  forms  of  the  Orsat  apparatus  now  upon  the 
market. 

A  further  drawback  in  the  usual  forms  of  Orsat  apparatus 
is  to  be  found  in  the  rubber  bulbs  that  are  attached  to  the  level- 
cylinders  of  the  pipettes  to  protect  the  various  reagents  from 
the  air.  These  bulbs  rapidly  deteriorate,  and  after  short  use 
fail  to  accomplish  the  purpose  for  which  they  are  intended. 

In  the  hope  of  remedying  some  if  not  all  of  the  defects  of 
the  Orsat  apparatus  that  have  been  enumerated  above,  the 
author  has  designed  the  modification  shown  in  Fig.  48.* 

The  burette  B  has  a  capacity  of  somewhat  more  than  100  cc. 
and  is  graduated  from  a  point  near  the  bottom  upward  to  the 
stopcock  /.  This  stopcock  is  a  three-way  stopcock,  the  posi- 
tion of  which  is  shown  by  means  of  a  black  glass  H  fused  to 
its  outer  surface.  The  capillary  tube  connecting  /  with  the 
pipettes  and  with  the  stopcock  K  has  an  external  diameter  of 
7  mm.  and  an  internal  diameter  of  one  mm.  In  fusing  on  the 
branch  capillaries  that  extend  downward  to  the  three  pipettes, 
the  internal  diameter  of  the  capillary  should  at  no  point  be 
much  greater  than  one  mm.  if  the  apparatus  is  properly  made. 
The  three  absorption  pipettes  E,  F,  and  G  are  of  the  form  al- 
ready described,  and  are  filled  respectively  with  solutions  of 
potassium  hydroxide,  alkaline  pyrogallol,  and  ammoniacal 
cuprous  chloride.  They  are  connected  with  the  capillary  tube 
from  the  burette  by  means  of  pieces  of  soft,  black  rubber  tubing 
of  1.5  mm.  thickness  of  wall,  and  these  rubber  tubes  are  held 
in  place  by  wire  hooks  that  pass  through  the  blocks  behind  the 
joints,  and  have  threaded  ends  upon  which  small  set  screws  are 
placed.  This  method  of  attachment  renders  it  easily  possible  to 
remove  all  the  glass  parts  from  the  frame.  Into  the  open  ends 

xThe  apparatus  is  manufactured  by  Greiner  and  Friedrichs,  Stiitzerbach  in 
Thiiringen,  Germany. 


86 


GAS  ANALYSIS 


FIG.  48 


GAS  ANALYSIS  OVER  WATER  87 

of  the  three  level-tubes  of  the  pipettes  are  inserted  one-hole 
rubber  stoppers,  and  through  the  openings  of  these  stoppers 
pass  the  branch  tubes  from  the  tube  SS  that  is  7  mm.  external 
diameter,  and  one  mm.  thickness  of  wall.  This  tube  passes 
downward  and  is  joined  by  a  piece  of  rubber  tubing  to  the  upper 
side  of  the  stopcock  attached  to  the  cylindrical  vessel  T  which 
in  turn  is  connected  with  V  by  the  glass  tube  shown  by  the 
dotted  line.  After  the  pipettes  have  been  filled  with  the  several 
reagents,  the  stoppers  connecting  the  level-tubes  with  the 
tube  SS  are  inserted  in  place  and  the  protecting  reservoir  VT 
is  half  filled  with  water.  As  the  gas  is  driven  over  from  the 
burette  into  the  pipette  and  is  drawn  back  into  the  burette, 
the  water  in  VT  rises  and  falls,  but  protects  the  reagents  at 
all  times  from  contact  with  the  air.  The  level-bottle  L  is  held 
in  place  by  a  clamp  when  the  apparatus  is  in  transport. 

Manipulation  of  the  Orsat  Apparatus.  —  The  level-bottle  L 
is  filled  with  water  which  is  then  driven  up  to  the  top  of  the 
burette  B  by  turning  the  stopcock  /  to  the  position  shown  in 
the  figure  and  raising  L.  The  stoppers  of  the  level-tubes  of 
the  pipettes  E,  F,  and  G  are  then  removed  and  the  solutions 
of  the  reagents  that  are  to  be  used  in  the  three  pipettes  are 
introduced  into  the  level-tubes.  The  stopcock  /  is  then  turned 
so  that  the  burette  B  is  in  communication  with  the  capillary 
tube  above  the  pipettes  and  the  liquid  in  each  pipette  is  drawn 
up  almost  to  the  lower  side  of  the  stopcock  by  turning  the  stop- 
cock to  position  II,  Fig.  47,  and  lowering  the  level-bottle  L. 
The  stopcock  of  each  pipette  is  closed  when  the  absorbing  liquid 
in  it  has  been  raised  to  this  point.  Water  is  now  poured  into 
the  reservoir  V  until  V  and  T  are  half  filled.  The  stoppers 
attached  to  the  branch  tubes  of  the  tube  55  are  then  inserted 
into  the  necks  of  the  level-tubes  of  the  pipettes. 

The  stopcock  J  is  now  turned  to  the  position  shown  in  Fig.  48 
and  the  water  in  the  burette  B  is  allowed  to  run  back  into  the 
level-bottle  L  and  is  then  poured  out  of  L.  The  level-bottle  is 
then  filled  with  water  that  has  been  saturated  with  the  gas 


88  GAS  ANALYSIS 

mixture  that  is  to  be  analyzed  (see  p.  59),  and  the  burette  B 
is  filled  with  this  confining  liquid  up  to  the  mark  on  the  capil- 
lary just  below  the  stopcock  J.  The  tube  N  is  now  connected 
with  the  pipe  or  gasometer  from  which  the  sample  of  gas  is  to 
be  drawn,  the  stopcock  K  is  opened  and  somewhat  more  than 
100  cubic  centimeters  of  the  sample  is  drawn  into  the  burette  B. 
The  stopcock  K  is  then  closed  and  exactly  100  cubic  centimeters 
of  gas  is  measured  off  in  B  in  the  manner  described  on  p.  59, 
the  excess  pressure  being  released  by  turning  /  to  the  position 
shown  in  the  figure.  The  stopcock  /  is  then  turned  to  such 
position  that  the  burette  B  communicates  with  the  absorption 
pipette  E,  the  level-bottle  L  is  raised  and  the  stopcock  of  the 
pipette  is  carefully  turned  to  position  II,  Fig.  47,  and  a  small 
amount  of  gas  just  sufficient  to  drive  the  absorbent  downward 
out  of  the  left  hand  capillary  tube  below  the  stopcock  is  allowed 
to  enter  the  pipette.  The  stopcock  is  then  turned  to  position  I, 
Fig.  47,  and  the  gas  sample  is  driven  over  from  the  burette 
into  the  pipette  at  such  speed  that  the  total  sample  will  pass 
into  the  pipette  in  about  two  minutes.  The  stopcock  of  the 
pipette  is  then  turned  to  position  II,  Fig.  47,  and  the  gas,  which 
now  occupies  the  space  FF,  Fig.  47,  is  drawn  back  into  the  bu- 
rette by  lowering  the  level-bottle,  the  liquid  in  the  pipette  being 
carefully  drawn  up  into  the  two  capillary  tubes  below  the  stop- 
cock until  it  stands  just  below  the  stopcock  in  each  tube.  The 
stopcock  is  then  closed.  In  the  determination  of  carbon  dioxide 
a  single  passage  of  the  gas  into  the  pipette  suffices  for  the  com- 
plete removal  of  the  constituent,  and  the  diminution  in  volume 
is  read  in  the  burette  B  after  the  water  has  been  allowed  to 
run  down  for  two  minutes.  In  the  absorption  of  oxygen  by 
alkaline  pyrogallol  and  of  carbon  monoxide  by  ammoniacal 
cuprous  chloride,  it  is  necessary  to  pass  the  gas  twice  through 
the  pipette.  In  such  case,  by  suitable  manipulation  of  the 
stopcocks,  the  gas  sample  after  being  drawn  back  from  the 
pipette  the  first  time  is  immediately  passed  through  it  a  second 
time.  In  the  determination  of  the  two  gases  in  question  the 


GAS  ANALYSIS   OVER  WATER  89 

second  passage  of  the  sample  may  be  more  rapid  than  the  first 
(about  one  minute).  The  sample  is  then  drawn  back  into  the 
burette  B  and  is  measured  in  the  usual  manner,  the  water  being 
allowed  to  run  down  one  minute  before  each  final  reading. 

After  the  absorption  of  the  first  constituent  in  the  pipette  E, 
the  second  is  absorbed  in  F  and  the  third  in  G.  The  three  gases 
that  are  most  usually  determined  with  the  Orsat  apparatus 
are  carbon  dioxide,  oxygen  and  carbon  monoxide  in  the  order 
named.  The  pipette  E  contains  potassium  hydroxide  (see  p.  2  25) , 
F  contains  alkaline  pyrogallol  (see  p.  160),  and  G  is  filled  with 
ammoniacal  cuprous  chloride  (see  p.  232).  If  the  gas  residue 
contains  combustible  constituents  that  are  to  be  determined, 
the  combustion  apparatus  is  connected  with  the  capillary  tube  M 
and  the  gas  in  the  burette  B  is  driven  into  the  combustion  pi- 
pette by  turning  the  stopcock  /  to  the  position  shown  in  Fig.  48 
and  raising  the  level-bottle  L.  If  only  a  portion  of  the  residue 
is  to  be  used  for  analysis  by  explosion,  the  larger  part  of  the 
gas  residue  may  be  passed  into  the  pipette  E.  The  smaller  por- 
tion of  the  gas  that  is  to  be  exploded  is  then  measured  in  B, 
the  stopcock  /  is  turned  to  the  position  shown  in  Fig.  48  and 
air  is  drawn  in  through  M  until  the  total  gas  volume  amounts 
to  nearly  100  cc.  /  is  then  closed,  the  explosion  pipette  is  con- 
nected to  M  and  the  mixture  of  combustible  gas  and  air  is 
driven  over  into  the  pipette. 

The  case  containing  the  apparatus  is  57  cm.  high,  27  cm. 
wide  and  16  cm.  deep.  The  panels  forming  the  front  and  back 
of  the  case  are  removed  when  the  apparatus  is  in  use.  As 
illustrative  of  the  accuracy  and  uniformity  of  the  results 
yielded  by  this  apparatus  the  following  analyses  of  a  mixture 
of  carbon  dioxide,  oxygen,  and  carbon  monoxide  may  be  cited. 

I  II  III  IV 

Carbon  dioxide,  per  cent               3.1  3.1  3.2  3.1 

Oxygen                                             6.0  6.0  5.9  5.9 

Carbon  monoxide,     "                 22.5  22.6  22.6  22.7 


CHAPTER  VII 

THE  HEMPEL  APPARATUS  FOR  EXACT  GAS  ANALYSIS 
WITH  MERCURY  AS  THE  CONFINING  LIQUID 

On  account  of  the  solubility  of  gases  in  water  no  great  accuracy 
is  attainable  when  this  is  used  as  the  confining  liquid  even  when 
it  is  saturated  with  the  gas  mixture  being  analyzed.  If  very 
accurate  results  are  desired,  the  apparatus  must  unquestionably 
be  filled  with  mercury.  Some  years  ago  it  was  difficult  to  obtain 
glass  stopcocks  that  were  perfectly  tight,  but  the  manufacture 
of  glass  apparatus  has  been  so  greatly  improved  of  late  that 
satisfactory  instruments  can  now  easily  be  procured.  Com- 
plete certainty  that  the  apparatus  is  absolutely  tight  is,  how- 
ever, assured  only  by  the  use  of  apparatus  that  contains  no 
stopcocks  or  rubber  connections  whatever,  and  in  which  all 
joints  are  made  by  fusing  the  glass  tubes  together. 

A.   APPARATUS  WITH  RUBBER  CONNECTIONS  AND 
GLASS   STOPCOCKS 

I.  Gas  Burettes  with  Correction  for  Variations  in  Temperature  and 
Barometric  Pressure 

Pettersson  1  was  the  first  to  show  that  by  means  of  a  tube 
inclosing  a  volume  of  gas  it  is  easy  to  compensate  the  error  which 
would  result  from  variations  in  the  pressure  and  temperature 
of  the  atmosphere.  Extreme  accuracy  in  gas  analysis  can  be  at- 
tained by  the  use  of  apparatus  that  is  filled  with  mercury  and  is 
provided  with  such  a  compensating  tube,  the  results  with  such 
an  instrument  being  quite  as  exact  as  those  obtained  with  the 
more  elaborate  apparatus  for  exact  gas  analysis  described  on 

1  Zeitschrift  fur  andytische  Chemie,  25  (1886),  467. 
90 


GAS  ANALYSIS  OVER  MERCURY  91 

p.  99,  provided  always  that  the  stopcocks  and  rubber  connections 
are  perfectly  tight.  Three  different  forms  of  gas  apparatus  with 
temperature  and  pressure  correction  are  shown  in  Fig.  49,  the 
measuring  tubes  being  varied  to  accommodate  gas  volumes 
of  different  sizes.  Fig.  49,  I,  shows  the  apparatus  intended 
for  the  measurement  of  gas  volumes  up  to  100  cc.  Fig.  49, 


FIG.  49 

II,  may  conveniently  be  used  when  the  gas  volume  amounts 
to  about  150  cc.  In  Fig.  49,  III,  is  shown  an  instrument  which 
was  specially  constructed  for  the  examination  of  gases  evolved 
from  bacteria,  the  gas  volumes  here  usually  not  exceeding  10  cc. 

The  instruments  consist  of  the  graduated  measuring  tubes  A, 
the  correction  tubes  B,  the  manometer  tubes  F,  and  the  level- 
bulbs  G.  The  measuring  tubes  and  level-bulbs  are  mounted 
in  suitable  iron  feet.  The  measuring  tubes  and  the  correction 


92  GAS  ANALYSIS 

tubes  stand  in  the  wide  glass  cylinders  C,  which  are  filled  with 
water  to  insure  that  these  two  tubes  are  at  all  times  at  the  same 
temperature.  The  measuring  tubes  are  closed  at  the  top  by  a 
double  Greiner-Friedrichs  glass  stopcock,  the  construction  of 
which  is  shown  in  Fig.  49,  IV. 

The  correction  tube  B  and  the  manometer  tube  F  are  made 
from  plain  glass  tubes  fused  together  in  the  form  shown  in  the 
cut.  g  is  a  small  capillary  tube.  The  manometer  tubes  are 
U-shaped,  and  are  somewhat  widened  at  k  and  i,  these  two 
widened  portions  having  marks  scratched  on  the  glass  at  exactly 
the  same  height.  The  manometer  tube  is  joined  to  the  measur- 
ing tube  by  means  of  a  piece  of  rubber  tubing  connecting  the 
end  of  the  capillary  /  with  the  tube  a  of  the  stopcock.  The 
reason  for  making  the  manometer  tube  so  long  lies  in  the  fact 
that  otherwise,  if  the  apparatus  is  carelessly  handled,  the  mer- 
cury might  easily  be  driven  from  the  manometer  tube  into  the 
burette  or  the  correction  tube.  With  the  arrangement  shown 
in  the  figure  this  is  almost  impossible,  since  the  difference  in 
pressure  must  be  more  than  half  an  atmosphere  before  the 
mercury  can  pass  over  into  either  tube.  The  manometer  tube  is 
made  completely  of  glass  to  prevent  the  mercury  being  con- 
taminated with  the  dirt  from  the  interior  of  a  rubber  connection. 
If  the  burette  has  become  dirty,  the  manometer  tube  is  removed, 
and  the  rest  of  the  instrument  may  then  be  cleaned  without  dan- 
ger of  any  change  taking  place  in  the  gas  volume  inclosed  in 
the  correction  tube. 

To  prepare  the  apparatus  for  use,  draw  some  distilled  water 
through  the  capillary  g  into  the  correction  tube  B,  and  also 
moisten  the  walls  of  the  measuring  tube  A  with  a  drop  or  two 
of  water.  Fill  the  level-bulb  G  with  mercury,  and  turn  the  glass 
stopcock  to  the  position  shown  in  DI.  Then  by  raising  the 
level-bulb  drive  the  mercury  over  into  the  manometer  tube 
until  the  latter  is  filled  up  to  the  marks  on  k  and  i. 

Before  proceeding  with  the  analysis,  the  volume  of  the  mano- 
meter tube  from  the  mark  on  k  to  the  point  a  must  be  ascertained. 


GAS   ANALYSIS  OVER  MERCURY  93 

To  do  this,  draw  over  the  mercury  in  the  manometer  until  it 
reaches  #,  then  turn  the  stopcock  D  until  it  has  the  position  of 
DZ,  and  now  draw  any  desired  volume  of  air  into  the  burette. 
Leaving  the  stopcock  open,  read  off  this  volume  of  air  on  the 
scale  of  the  burette,  the  air  here  being,  of  course,  under  the  pre- 
vailing pressure  of  the  atmosphere.  Turn  stopcock  D  so  that 
the  burette  communicates  with  the  manometer  tube,  and  drive 
the  air  over  into  this  latter  tube  until  the  mercury  in  it  stands 
at  equal  height  in  its  two  branches;  that  is,  at  the  marks  on  k 
and  i.  The  difference  between  the  two  readings  on  the  measur- 
ing tube,  provided  the  tube  g  remains  open,  gives  the  volume 
of  the  manometer  from  the  mark  on  k  up  to  a. 

Correction  tube  B  may  be  used  in  either  of  two  ways.  We 
may  inclose  within  it  an  indeterminate  amount  of  air  by  simply 
fusing  together  the  end  of  the  tube  g  so  that  the  volume  in  the 
correction  tube  will  correspond  to  the  barometric  pressure  and 
temperature  prevailing  at  the  time  of  operation,  or  we  may  fill 
B  with  such  an  amount  of  air  that  the  apparatus  will  indicate 
directly  gas  volumes  reduced  to  standard  conditions  —  that  is, 
to  o°  C.  and  760  mm.  pressure.  In  the  latter  case,  the  gas  will 
have  at  the  ordinary  temperature  of  the  room  a  pressure  some- 
what above  that  of  the  atmosphere.  In  the  former  case  the  ba- 
rometer and  the  thermometer  must  be  read  at  the  time  the  tube  g 
is  fused  together,  so  that  we  may  be  able  to  correct  gas  volumes 
whenever  this  is  necessary. 

In  many  cases  it  is  highly  desirable  to  so  arrange  the  ap- 
paratus that  the  reading  on  the  measuring  tube  A  corresponds 
directly  to  volumes  at  o°  C.  and  760  mm.  pressure.  To  accom- 
plish this  a  piece  of  rubber  tubing  is  slipped  over  the  end  of  the 
capillary  tube  g  and  fastened  firmly  in  place  by  a  wire  ligature. 
By  lowering  the  level-bulb,  mercury  is  drawn  over  into  the 
manometer  tube  until  it  reaches  the  capillary  I,  and  the  burette 
is  then  allowed  to  stand  for  two  hours  in  a  room  of  fairly  con- 
stant temperature.  The  stopcock  D  is  then  opened  so  that  the 
contents  of  the  burette  are  in  free  communication  with  the 


94  GAS  ANALYSIS 

atmospheric  air.  As  soon  as  one  is  convinced  that  all  parts 
of  the  apparatus  are  at  the  same  temperature,  the  gas  volume 
in  the  burette  is  read  exactly,  and  the  temperature  and  baro- 
metric pressure  are  noted.  The  thermometer  and  barometer 
should  stand  in  the  same  room  with  the  apparatus.  The  stop- 
cock D  is  closed  and  the  volume  which  the  gas  would  occupy 
at  o°  C.  and  760  mm.  barometric  pressure  is  now  calculated. 

Example.  —  The  gas  volume  is  97  cc.,  the  barometric  pres- 
sure 753.3  mm.,  and  the  temperature  8.75°  C.  The  space  from 
k  to  a  in  the  manometer  has  previously  been  determined  and 
found  to  be  1.8  cc.  The  tension  of  the  water  vapor  at  8.75°  C. 
is  8.4  mm.  The  corrected  volume  is  92.1  cc. 

Since,  however,  in  making  measurements  with  the  correction 
tube,  the  gas  fills  the  space  from  k  to  a,  this  volume  must  be 
subtracted  from  the  above  result:  — 

92.1  -  1.8  =  90.3  cc. 

In  order  now  to  adjust  the  gas  volume  in  the  correction  tube 
so  that  readings  of  volumes  in  the  burette  will  be  reduced  at 
once  to  standard  conditions,  the  stopcock  D  is  turned  so  that 
the  burette  communicates  with  the  manometer  tube,  and  the 
gas  in  the  burette  is  compressed  by  raising  the  level-bulb  G 
to  the  volume  which  it  has  been  calculated  that  it  would 
occupy  at  o°  C.  and  760  mm.  pressure.  The  mercury  in  the 
manometer  tube  is,  of  course,  forced  out  of  equilibrium  by  this 
operation.  Air  is  now  blown  into  the  correction  tube  through 
the  rubber  tube  at  g  until  the  mercury  stands  at  the  same  height 
in  the  two  branches  of  the  manometer  tube,  and  the  rubber 
tube  is  then  closed  by  means  of  a  strong  pinchcock  placed  di- 
rectly above  the  end  of  g. 

A  rubber  tube  cannot  remain  tight  for  any  length  of  time, 
and  therefore  the  glass  tube  g  must  be  fused  together.  This 
cannot  be  done  at  once  because  of  the  high  pressure  of  the  air  in 
the  correction  tube,  but  the  operation  may  easily  be  performed 
by  first  removing  the  rubber  tube  joining  the  manometer  tube 


GAS   ANALYSIS   OVER   MERCURY  95 

with  the  burette  at  a  and  then  placing  the  correction  tube  B 
in  a  freezing  mixture  of  salt  and  ice,  allowing  it  to  stand  therein 
until  the  mercury  in  the  manometer  shows  that  the  pressure 
on  the  inside  of  the  correction  tube  is  smaller  than  that  of  the 
external  atmosphere.  The  tube  g  can  now  be  heated  by  means 
of  a  blast  lamp  and  drawn  out  and  fused  together  directly  be- 
low the  rubber  tube  which  is  upon  it. 

There  is  danger  that  the  glass  tube  g  may  crack  when  it  is 
heated.  This  can  be  avoided  by  painting  it  with  a  thin  emul- 
sion of  Plaster  of  Paris  stirred  up  with  water,  leaving  the  place 
where  the  tube  is  to  be  drawn  out  uncovered  by  this  coating. 
The  Plaster  of  Paris  offers  an  excellent  protection  against  the 
overheating  of  that  part  of  the  glass  tube  which  it  is  not  desired 
to  soften  and  can  afterward  easily  be  removed  with  the  aid  of 
water. 

The  correction  tube,  after  being  thus  adjusted,  is  again  joined 
to  the  burette.  The  readings  of  gas  volumes  in  the  burette 
now  give  directly  the  volumes  under  standard  conditions,  no 
matter  how  great  may  be  the  variations  of  temperature  and 
pressure,  provided  always  that  in  making  the  measurements 
the  stopcock  is  turned  to  the  position  of  D\  and  the  mercury 
in  the  manometer  tube  is  brought  to  the  marks  k  and  i  by  ex- 
panding or  compressing  the  gas  in  the  measuring  tube.  The 
exact  adjustment  of  the  mercury  in  the  manometer  tube  is 
effected  by  raising  or  lowering  the  level-bulb  G  until  the  mercury 
stands  nearly  at  the  marks  k  and  i,  then  closing  the  stopcock  n 
and  turning  the  screw  o  so  as  to  exert  greater  or  less  pressure  on 
the  piece  of  rubber  tubing  against  which  it  plays.  This  piece  of 
rubber  tubing,  as  is  shown  in  the  figure,  connects  the  lower  end 
of  the  burette  with  the  stopcock  n.  In  this  manner  the  surface 
of  the  mercury  in  the  two  arms  of  the  manometer  may  be  brought 
exactly  to  the  same  level.  This  style  of  adjustment  is  original 
with  Pettersson  and  enables  us  to  effect  slight  changes  in  the 
size  of  the  gas  volume  in  a  most  convenient  and  rapid  manner. 
In  all  cases  where  rubber  tubing  must  withstand  considerable 


96  GAS  ANALYSIS 

pressure  it  is  desirable  to  use  enamelled  rubber  tubing  which, 
although  not  quite  as  elastic  as  the  ordinary  kind,  will  easily 
withstand  a  pressure  of  several  atmospheres. 

//.  The  Absorption  Pipettes 

On  account  of  the  great  differences  in  pressure  caused  by  col- 
umns of  mercury  of  only  moderate  height  it  becomes  necessary 


FIG.  50 

to  give  to  these  absorption  pipettes,  which  are  partially  filled 
with  mercury,  a  form  somewhat  different  from  that  adopted 
for  the  pipettes  containing  aqueous  solutions. 

The  Simple  Mercury  Absorption  Pipette 

This  consists  of  two  bulbs,  a  and  b,  Fig.  50,  joined  together 
by  a  piece  of  enamelled  rubber  tubing.  The  bulb  a  has  a  capacity 
of  about  130  cc.  and  b  a  capacity  of  about  150  cc. 


GAS  ANALYSIS   OVER   MERCURY 


97 


The  Simple  Mercury  Absorption  Pipette  for  Solid  and  Liquid 

Reagents 

This  resembles  the  pipette  just  described,  except  that  the 
bulb  b,  Fig.  51,  is  cylindrical  in  form  and  has  at  its  lower  ex- 
tremity a  cylindrical  neck,  i,  through  which  the  bulb  can  be 
filled  with  solid  substances,  i  is  then  closed  with  a  cork  or 
rubber  stopper  held  in  place  by  a  wire  ligature. 


FIG.  51 


The  Mercury  Absorption  Pipette  with  Absorption  Bulb 

This  pipette  has  in  addition  to  the  two  bulbs  a  and  b,  Fig.  52, 
a  third  bulb  c  filled  with  broken  glass  or  with  glass  beads.  The 
advantage  of  this  small  bulb  lies  in  the  fact  that  when  the  gas 
is  driven  over  into  the  pipette,  the  reagent  which  the  latter 
contains  clings  to  the  small  pieces  of  glass  in  c,  and  causes  a 


98 


GAS  ANALYSIS 


more  complete  absorption  of  that  constituent  of  the  gas  mix- 
ture which  is  to  be  removed.  The  pipette  has,  however,  one 
drawback:  with  viscous  reagents  bubbles  of  gas  are  liable  to 
cling  to  the  broken  glass  in  c. 

The  mercury  pipettes  are  manipulated  in  exactly  the  same 
manner  as  the  pipettes  for  aqueous  solutions  above  described, 
except  that  here  only  small  quantities  of  the  reagent  are  em- 
ployed in  crder  to  reduce  the  error  that  is  caused  by  the  solu- 


FIG.  52 

bility  in  the  reagent  of  those  gases  which  are  not  directly  ab- 
sorbed by  it.  This  erjor  can  be  still  further  lessened  by  intro- 
ducing into  the  gas  pipette  an  amount  of  reagent  sufficient  for 
two  analyses  of  the  gas  mixture  in  question.  In  the  first  analysis 
the  reagent  becomes  saturated  with  those  gases  for  which  it  is 
not  an  absorbent,  and  the  error  due  to  solution  of  the  gases  in 
the  reagent  is  thus  minimized  in  the  second  analysis.  The  re- 
agents are  introduced  into  the  gas  pipette  by  means  of  a  small 
pipette  inserted  in  the  rubber  tube  b. 


GAS  ANALYSIS  OVER  MERCURY  99 


B.   APPARATUS     FOR     EXACT     GAS     ANALYSIS     WITHOUT     RUBBER 
CONNECTIONS   OR   STOPCOCKS 

Experience  has  shown  that  even  the  best  glass  stopcocks 
cannot  be  relied  upon  with  certainty  for  any  considerable 
length  of  time,  and  rubber  connections  will  allow  small  quanti- 
ties of  gas  gradually  to  pass  through  them.  It  is  therefore 
apparent  that  an  apparatus  which  contains  no  stopcocks  or 
rubber  connections  whatever  possesses  decided  advantages 
over  one  in  which  errors  arising  through  leakage  are  liable  to 
occur. 

The  wonderfully  simple  and  exact  gasometric  methods  de- 
vised by  Bunsen  fulfill  completely  these  demands,  but  unfortu- 
nately the  rapid  performance  of  a  large  number  of  exact  analyses 
is  not  possible  with  his  apparatus. 

The  method  devised  by  Doyere  *  resembles  that  of  Bunsen, 
in  that  the  analysis  is  carried  out  in  glass  vessels  fused  together, 
and  all  ground  joints  and  rubber  connections  are  avoided:  it 
has,  however,  the  fault  that  great  accuracy  can  be  obtained 
only  by  the  use  of  very  cumbersome  apparatus. 

By  the  introduction  of  a  different  manner  of  measuring  and 
a  somewhat  changed  construction  of  the  necessary  absorption 
pipettes,  Hempel  has  endeavoured  to  improve  the  Doyere 
method,  so  that,  in  its  changed  form,  rapid  and  very  exact 
work  may  be  possible  without  the  use  of  delicate  physical  in- 
struments. 

Bunsen  measures  the  gases  under  varying  pressure  and  vary- 
ing volume,  and  Doyere  measures  them  under  constant  pres- 
sure and  varying  volume,  while  in  the  method  about  to  be 
described  the  measurements  are  made  under  constant  volume 
and  varying  pressure.  Following  Boyle's  law,  the  values  so 
found  bear  the  same  proportion  to  one  another  as  do  gas 
volumes  under  the  same  pressure. 

1  Ann.  chim.  phys.  [3]  28,  (1850),  p.  i. 


ioo  GAS  ANALYSIS 

Doyere  1  measures  the  gases  in  a  Bunsen  eudiometer,  and 
he  avoids  correction  for  pressure  by  joining  the  eudiometer 
with  an  iron  holder  having  a  screw  attachment,  by  means  of 
which  the  mercury  in  the  tube  and  in  the  suitably  formed  trough 
may  be  brought  to  the  same  level.  The  readings  are  made 
with  a  special  telescope  of  great  exactness.  The  absorptions 
are  effected  in  Doyere's  improved  Ettling  gas  pipette. 

The  manipulation  of  the  pipettes  demands  that  the  eudi- 
ometer at  some  place  in  the  mercury  trough  be  brought  wholly 
beneath  the  level  of  the  mercury,  and  further,  that  the  suction 
tubes  of  the  pipettes  be  as  long  as  the  eudiometer.  From  these 
two  particulars  it  results  that  when  a  very  deep  trough  is  used, 
the  pipettes  are  very  unwieldy  and  easily  broken,  or  that  when 
a  shorter  eudiometer  is  employed,  a  sharp  reading  of  the  scale 
can  be  made  only  with  the  most  perfect  instruments,  since  it 
must  be  possible  to  measure  with  exactness  tenths  of  a  milli- 
meter. 

Doyere  states  that  the  measuring  tubes  used  by  him  have  a 
length  of  20  cm.  and  an  internal  diameter  of  15  mm.  For  large 
gas  volumes  he  uses  vessels  similar  to  those  employed  by  Bunsen 
for  this  purpose,  the  lower  part  being  cylindrical  and  gradu- 
ated, and  ending  above  in  a  bulb. 

The  method  here  to  be  described  permits,  by  the  employ- 
ment of  spherical  measuring  vessels,  the  use  of  a  shallow  mer- 
cury trough  and  of  shorter,  more  easily  manipulated,  and  less 
fragile  gas  pipettes,  and  a  measurement  more  than  three  times 
as  sharp,  since  with  this  apparatus,  if  the  gas  at  the  beginning 
of  the  analysis  nearly  fills  the  bulb  at  atmospheric  pressure,  the 
scale  has  an  available  length  of  760  mm.  while  Doyere's  measur- 
ing tube  is  only  200  mm.  long. 

The  measurements  are  made  at  constant  volume,  varying 
temperature,  and  varying  pressure.  This  is  accomplished  by 
placing  the  gas  in  small  glass  bulbs  which  can  easily  be  brought 
into  communication  with  the  manometer  tube,  by  then  ex- 

1  Loc.  cit.,  also  Fehling's  Handw'drterbuch  der  Chemie,  vol.  i,  p.  512. 


GAS  ANALYSIS  OVER  MEfc£URl?,J        ,:i>tii> 

panding  the  gas  to  a  certain  volume  by  lowering  a  movable 
vessel  filled  with  mercury,  and  finally  reading  on  the  manom- 
eter tube  the  pressure  under  which  the  gas  now  stands.  Ac- 
cording to  Boyle's  law  the  values  thus  obtained  bear  the  same 
proportion  to  one  another  as  do  gas  volumes  under  the  same 
pressure. 

The  absorptions  are  effected  in  gas  pipettes  to  be  described 
later. 

THE  MEASURING  APPARATUS 

This  (Fig.*  53)  consists  of  an  iron  mercury  trough  A  (on  ac- 
count of  the  presence  of  water,  wood  cannot  be  used,  since  it 
would  swell  and  change  form),  of  a  glass  tube  D  graduated  in 
millimeters  and  from  76  to  80  cm.  long  and  further,  of  the 
wooden  stand  G  and  the  water  reservoir  E.  The  sides  of  the 
water  reservoir  E  are  glass  panes,  one  of  which  e  extends  only  so 
deep  into  the  mercury  as  to  leave  room  to  bring  the  capillary 
of  the  pipette  B  under  it  into  the  measuring  bulb  C. 

By  placing  the  measuring  bulb  upon  the  rubber  stopper  a 
in  the  mercury  trough  it  can  always  be  brought,  by  means  of 
the  holder/,  into  mercury- tight  connection  with  the  graduated 
tube  D.  The  tube  b  and  the  J_-piece  d  are  made  of  iron.  D  is 
connected  with  an  arm  of  d  by  means  of  a  piece  of  enamelled 
rubber  tubing,  or  ordinary  rubber  tubing  so  wrapped  as  to 
enable  it  to  resist  the  pressure  of  the  mercury.  A  piece  of 
enamelled  rubber  tubing  joins  the  other  arm  to  the  movable 
level-bulb  H,  but  between  d  and  m  there  is  introduced  the 
Pettersson  device  for  the  fine  adjustment  of  the  mercury.  (See 
Fig.  106.) 

In  making  the  measurement,  the  measuring  bulb  C  is  brought 
into  the  position  shown  in  Fig.  53,  and  is  pressed  down  tightly 
upon  the  rubber  stopper  a  by  means  of  the  clamp  /.  Mercury 
is  then  drawn  out  through  d  until  the  meniscus  of  the  mercury 
in  the  measuring  bulb  lies  nearly  tangent  to  the  horizontal  hair 
of  a  magnifying  glass  which  is  fastened  to  the  apparatus  op- 


FIG.  53 


GAS  ANALYSIS  OVER   MERCURY  103 

posite  /.  This  glass  is  not  shown  in  the  figure,  m  is  then  closed 
and  the  exact  adjustment  of  the  height  of  the  mercury  at  /  is 
effected  by  turning  the  screw  n. 

The  height  of  the  mercury  in  the  manometer  tube  D  is  now 
read  with  a  cathetometer,  and  the  pressure  of  the  gas  in  the 
bulb  is  then  calculated. 

Since  the  space  in  the  bulb  is  kept  saturated  with  water 
vapor  by  moisture  in  the  bulb,  the  corrected  pressure  of  the 
gas  in  the  bulb  is  ascertained  by  use  of  the  equation 


in  which  b  is  the  observed  barometric  pressure,  m  the  pres- 
sure of  water  vapor  at  the  temperature  of  the  water  in  the 
reservoir  E,  and  d  the  pressure  in  the  manometer  D. 

THE   MEASURING   BULB 

The  measuring  bulb  E  (Fig.  54)  is  fastened  to  the  iron  holder 
g  by  means  of  the  projecting  tubes  r  and  s  .  r,  which  is  closed  at 
the  top,  is  about  5  mm.  long  and  s  about  30  mm.  At  from  5  to  7 
mm.  below  the  bulb,  5  is  widened  into  a  collar  x  by  softening 
the  glass  tube  in  the  blast-lamp  flame  and  pressing  it  together. 
The  iron  holder  g  has  at  t  a  thick  perforated  sheet-iron  cap  for 
holding  r.  The  holder  bends  around  the  bulb  and  is  supplied 
at  the  lower  end  with  the  perforated  iron  plate  u,  which  is  bent 
at  a  right  angle,  and  holds  the  projection  s.  u  may  be  set  where 
desired  by  means  of  the  screw  v,  to  which  the  slot  through  which 
it  passes  gives  a  play  of  several  millimeters.  5  projects  4  to 
5  mm.  beyond  the  plate  u.  The  iron  collar  y  is  fastened  to  g 
in  such  a  position  that  it  just  slips  under  the  fork  /  when  the 
holder  and  bulb  are  placed  over  the  end  of  the  iron  tube  passing 
through  the  rubber  stopper  m,  and  are  firmly  pressed  against 
the  rubber.  The  fork  is  firmly  fastened  to  the  slide  i,  which 
can  be  moved  up  and  down  by  the  screw  h.  By  screwing  the 
slide  down,  the  measuring  bulb  can  be  pressed  against  the  rub- 


IO4 


GAS  ANALYSIS 


her  stopper  and  a  tight  con- 
nection with  the  barometer  tube 
thus  be  obtained.  A  scale  upon 
the  slide  i  and  its  guides  makes 
it  possible  to  bring  the  bulb  at 
different  times  into  exactly  the 
same  position  as  regards  the 
millimeter  scale  of  the  ba- 
rometer. 

The  total  height  of  the  meas- 
uring bulbs  varies  from  7.5  to 
9.5  cm. 

Since  the  walls  of  the  measur- 
ing bulbs  are  only  as  thick  as 
those  of  ordinary  bulb  pipettes, 
it  was  thought  possible  that,  in 
the  measurement  of  very  small 
gas  volumes,  the  volume  of 
the  bulb  might  be  decidedly 
changed,  since  under  such  con- 
ditions it  is  exposed  to  nearly 
the  full  pressure  of  the  atmos- 
phere. 

To  settle  this  question,  Hem- 
pel  determined  the  volume  of 
the  bulb,  first  empty  and  then 
filled  with  gas,  in  a  stereometer, 
and  it  was  found  that  even  with 
large  bulbs  of  100  cc.  capacity 
no  measurable  difference  of  vol- 
ume could  be  detected;  hence 
even  thin-walled  glass  bulbs 
may  be  used  without  hesitation 
for  these  measurements. 

Curiously  enough,  it  is  quite 


GAS  ANALYSIS  OVER   MERCURY 


105 


difficult  to  lower  the  measuring  bulb  through  the  water  in  E 
(Fig.  53)  down  into  the  mercury  below  without  some  water 
getting  into  the  inside  of  the  bulb.  .  If  this  should  happen, 
exact  reading  would,  of  course,  be  impossible.  Tfye  operation 
can  be  performed,  however,  by  bringing  the  measuring  bulb 
into  two  porcelain  crucibles  placed  one  within  the  other  in  the 
manner  shown  in  Fig.  55,  and  then  filling  these  two  crucibles 
with  mercury.  When  these  are  lowered  through  the  water 
into  the  mercury  the  larger  crucible  A  is  first  removed,  and 
then  the  crucible  B  is  lowered  away  from  the  mouth  of  the 


FIG.  55 


FIG.  56 


bulb.    The  opening  in  the  bulb  is  now  below  the  surface  of 
the  mercury,  and  yet  no  water  has  entered  it. 

By  means  of  the  instrument  shown  in  Fig.  56  the  air  may  be 
sucked  out  of  the  measuring  bulb,  and  the  gas  sample  can  then 
be  transferred  to  the  bulb  by  means  of  one  of  the  pipettes  de- 
scribed below. 

GAS   PIPETTES   FOR   LIQUID   ABSORBENTS 

The  gas  pipettes  were  devised  by  Ettling  and  were  first  used 
by  Doyere  as  absorption  vessels  for  gas  analysis. 

They  consist  of  two  bulbs  a  and  b  (Fig.  57),  of  the  same  size, 
joined  together  by  the  tube  c  and  ending  in  the  bent  capillary 
tube  d.  A  very  small  bore  thermometer  tube,  and  not  a  tube 


io6 


GAS   ANALYSIS 


of  i  mm.  bore  as  Doyere  suggests,  is  used  as  the  capillary,  thus 
making  it  easy  to  avoid  introducing  absorbent  into  the  measur- 
ing bulb  or  leaving  any  considerable  quantity  of  gas  in  the 
pipette. 

Gases  move  rapidly  in  capillary  tubes,  but  liquids,  especially 
concentrated  solutions  of  salts,  move  very  slowly;  hence  it  is 
easily  possible  to  bring  the  gas  residue  in  the  pipette  to  less  than 
°f  a  cubic  centimeter  without  danger  of  the  absorbent  en- 
tering the  measuring 
bulb.  It  is  almost  im- 
possible to  do  this  when 
wider  glass  tubes  are 
used. 

The  pipettes  must 
be  so  made  that  the 
distance  a  (Fig.  57)  is 
only  as  large  as  or 
smaller  than  ft:  the 
capillary  must  be  bent 
close  to  the  bulb  b. 
The  pipettes  are  fas- 
tened to  the  wooden 
standard  in  such  a  po- 
sition that  the  capillary 
d  comes  to  within  a  few 
millimeters  of  the  bottom  of  the  mercury  trough  when  the 
pipette  is  placed  in  the  position  shown  in  Fig.  53. 

The  bulbs  of  the  pipettes  must  be  considerably  larger  than 
the  volume  of  the  gas  to  be  brought  into  them.  The  incon- 
venience of  carefully  cleaning  the  pipette  after  the  absorption 
is  avoided  by  using  a  special  pipette  for  each  reagent.  Pipettes 
of  very  different  sizes  are  employed,  the  sizes  depending  natu- 
rally upon  the  dimensions  of  the  measuring  bulbs. 

To  bring  a  measured  amount  of  the  absorbent  into  the  pi- 
pette, which  is  first  filled  with  mercury,  connect  it  by  means  of 


FIG.  57 


GAS  ANALYSIS  OVER  MERCURY 


107 


a  piece  of  rubber  tubing  e  (Fig.  39)  with  the  small  burette  / 
containing  the  reagent  and  supported  by  the  clamp  g.  Open 
the  pinchcock  h,  slip  a  rubber  tube  over  the  burette  at  i,  and 
by  suction  so  exhaust  the  air  in  the  burette  that  any  gas  re- 
maining in  the  pipette  will  be  drawn  through  the  capillary  x  and 
through  the  absorbent.  The  pipette  is  thus  completely  filled 
with  mercury.  Stop  the  suction  as  soon  as  the  mercury  is  visible 
above  the  rubber  e,  put  the  rubber  tube  on  the  pipette  at  /,  and 
draw  the  mercury  back  to  the  capillary.  Note  the  height  of 
the  absorbent  in  the  burette,  and  then  suck  the  desired  amount 
of  the  same  through  the  capillary  d  into  the  pipette.  At  the 
moment  when  the  necessary  amount  of  reagent  has  passed  over, 
bring  a  drop  of  mercury  into  the  burette  at  i. 

The  amount  of  the  absorbent  introduced  may  be  sharply  de- 
termined by  drawing  the  mercury  into  the  pipette  until  the 
reagent  is  again  visible  in  the  capillary  d,  and  then  noting  the 
height  of  the  reagent  in  the  burette. 

The  bent  capillary  tube  of  the  pipette  is  cleaned  and  freed 
from  all  traces  of  reagent  by  lowering  the  tube  into  a  beaker 
filled  with  distilled  water,  and  then  drawing  water  into  the 
capillary  and  driving  it  out  again  by  sucking  and  blowing  on  a 
rubber  tube  attached  to 
the  open  end  of  a. 

The  pipette  thus  pre- 
pared for  the  analysis  con- 
tains mercury  between  v 
and  w,  between  w  and  x 
the  absorbent,  and  from  x 
to  y  mercury  (Fig.  39). 

GAS  PIPETTES  FOR  SOLID 
ABSORBENTS 


To  bring  the  gases  un- 
der examination  into  con- 
tact with  solid  absorbents, 


FIG.  58 


loS 


GAS  ANALYSIS 


the  form  of  pipette  shown  in  Fig.  58  is  used.  In  this  the 
tube  c  has  a  branch  tube  e  through  which  solid  substances, 
such  as  sticks  of  phosphorus,  are  introduced  into  the  bulb  b; 


FIG.  59 

e  is  then  closed  at  /  with  a  cork,  and  the  pipette  is  filled  as 
usual  with  mercury.  When  a  gas  is  drawn  in,  the  solid  sub- 
stances remain  in  the  bulb  b,  and  so  come  into  contact  with 
the  gas. 


GAS  ANALYSIS  OVER   MERCURY  109 


THE   ABSORPTION 

The  gas  pipettes  already  described  are  used  for  the  absorp- 
tions, the  manipulation  being  shown  in  Fig.  59  and  Fig.  60. 

Figure  59  gives  the  position  in  which  it  is  possible  to  bring 
the  gas  completely  into  the  pipette.  The  measuring  bulb  is 
here  brought  below  the  surface  of  the  mercury  and  the  gas  is 
drawn  into  the  pipette  by  sucking  with  the  mouth  on  a  rubber 
tube  attached  to  m.  The  suction  is  discontinued  at  the  moment 
when  the  mercury  begins  to  flow  from  the  capillary  into  the 
bulb  of  the  pipette. 

The  pipette  then  contains  (see  Fig.  57)  mercury  from  v  to 
w,  absorbent  from  w  to  x,  gas  from  x  to  g,  and  mercury  from  g 
to  z,  so  that  the  pipette,  after  it  is  taken  out  of  the  mercury 
trough,  may  be  vigorously  shaken  and  a  rapid  absorption  ef- 
fected. 

To  drive  the  gas  from  the  pipette  back  again  into  the  measur- 
ing bulb,  the  apparatus  is  brought  into  the  position  shown  in 
Fig.  60. 

In  the  beginning  it  is  necessary  to  blow  into  the  pipette  at 
m  to  set  the  gas  in  motion;  when  it  has  once  started,  the  mer- 
cury in  the  measuring  bulb  acts  with  an  aspirating  effect,  so 
that  the  gas  passes  over  of  itself.  At  the  moment  when  the 
absorbent  has  risen  to  about  i  cm.  from  the  end  of  the 
capillary  in0  the  measuring  bulb,  the  capillary  is  lowered 
under  the  mercury,  and  mercury  is  drawn  into  the  capillary 
by  sucking  on  the  rubber  tube  attached  to  m.  In  this  manner 
the  entering  of  reagent  into  the  measuring  bulb  may  be  avoided 
with  certainty. 

If  a  gas  thread  about  i  cm.  long  remains  in  the  capillary, 
this  corresponds  to  approximately  o.ooi  cc.  of  gas,  since  the 
total  35  cm.  length  of  the  capillary  has  a  volume,  determined 
by  weighing  the  mercury  which  it  holds,  of  0.038  cc.  Conse- 
quently no  appreciable  error  arises  from  this  source. 

The  analysis  is  made  as  follows:  — 


no 


GAS  ANALYSIS 


Fill  the  carefully  cleaned  and  moistened  measuring  bulb 
with  the  gas  under  examination  by  lowering  the  bulb  into  the 
mercury  in  the  trough,  drawing  out  the  air  in  it  with  a  gas 


FIG.  60 


pipette,  and  bringing  the  gas  into  the  bulb  either  by  means  of 
a  delivery  tube  brought  under  the  mouth  of  the  bulb  or  by 
means  of  a  gas  pipette. 


GAS  ANALYSIS  OVER   MERCURY  in 

The  necessary  measurements,  absorptions,  and  explosions 
now  follow,  their  order  being  determined  by  the  nature  of  the  gas. 

Since  difficulties  arise  only  in  the  use  of  fuming  sulphuric 
acid  over  mercury,  while  all  other  reagents  can  easily  be  manip- 
ulated in  the  manner  already  described,  the  reader  is  referred 
to  Chapter  XIII  for  descriptions  of  methods  of  absorption  of 
the  various  gases. 

The  heavy  hydrocarbons  cannot  be  absorbed  with  fuming 
sulphuric  acid  in  the  manner  described,  because,  on  bringing  to- 
gether the  fuming  acid  and  mercury,  sulphur  dioxide  is  evolved 
even  in  the  cold,  and  acid  sulphates  are  formed  which,  upon 
long  standing,  separate  as  thick  crusts  and  obstruct  the  pipette. 
Since,  however,  the  gases  that  are  not  absorbable  by  the  fuming 
acid  are  very  insoluble  in  the  same,  a  pipette  completely  filled 
with  the  acid  may  be  used,  the  mercury  here  coming  into  con- 
tact with  the  sulphuric  acid  only  in  the  capillary  tube.  If  care 
be  taken  in  the  manipulation  that  no  mercury  passes  over  from 
the  trough  into  the  pipette,  and  if,  after  using,  all  mercury  be 
removed  from  the  capillary  by  means  of  a  common  suction 
pipette  attached  thereto,  so  that  sulphuric  acid  alone  remains 
in  the  pipette,  a  stoppage  of  the  capillary,  which,  when  it  has 
once  taken  place,  is  difficult  of  removal,  need  not  be  feared. 

To  protect  the  lungs  from  the  fumes  of  the  sulphuric  acid,  a 
glass  tube  filled  with  pieces  of  caustic  potash  is  interposed  be- 
tween the  rubber  suction  tube  and  the  pipette. 

Unless  very  accurate  results  are  desired,  it  is  sufficient  to 
make  all  readings  with  the  unaided  eye,  for  if  the  eye  be  brought 
only  approximately  to  the  same  plane  with  the  surface  of  the 
mercury  column  that  is  to  be  read,  the  results  thus  obtained 
are  quite  close  to  the  truth. 

The  accuracy  of  the  analysis  may  easily  be  greatly  increased 
by  using  a  number  of  measuring  bulbs  of  different  sizes  and 
determining  their  volumes  by  filling  them  with  mercury  and 
weighing  the  mercury.  The  gas  to  be  analyzed  is  then  first 


112  GAS  ANALYSIS 

brought  into  the  largest  bulb  and  one  or  more  of  its  constitu- 
ents are  determined.  If  the  remaining  volume  now  amounts 
to  only  a  half  or  two-thirds  of  the  original  volume,  this  residue 
is  introduced  into  a  smaller  measuring  bulb.  This  procedure 
permits  of  the  use  of  the  total  length  of  the  manometer  tube  D 
(Fig.  53)  in  making  the  measurements,  and  consequently  in- 
sures much  greater  accuracy  in  the  readings. 


CHAPTER  VIII 

THE  CONSTRUCTION  AND  CONNECTION  OF 
APPARATUS 

Glass  Blowing.  —  It  is  of  great  convenience  to  the  gas  ana- 
lyst to  be  able  to  make  simple  forms  of  glass  apparatus  and  to 
repair  broken  parts.  The  elements  of  glass  blowing  are  clearly 
described  in  such  books  as  that  by  Shenstone,  and  with  prac- 
tice it  is  possible  for  almost  every  chemist  to  develop  consider- 
able facility  in  glass  blowing. 

The  blast-lamp  should  have  cocks  on  the  lamp  itself  for  the 
easy  regulation  of  the  supply  of  gas  and  air  blast.  It  should 
give  with  full  blast  pressure  a  colorless  flame  about  thirty  cm. 
long,  and  with  diminished  blast  pressure  a  yellow-tipped  flame 
about  forty  cm.  long.  On  cutting  down  the  gas  and  air  pressure, 
the  lamp  should  furnish  a  small,  sharp  pointed,  colorless  flame 
about  five  cm.  long. 

The  glass  tubing  should  be  easily  fusible  and  the  ordinary 
sizes,  from  six  mm.  to  twenty  mm.  in  diameter,  should  have  a 
wall  about  one  mm.  thick.  Glass  tubes  or  glass  parts  that 
are  to  be  fused  together  should  be  of  the  same  kind  of  glass,  for 
joints  made  of  different  kinds  of  glass  will  usually  easily  break 
apart.  All  joints  should  be  highly  heated  and  thoroughly  blown 
out,  and  should  be  carefully  annealed  by  holding  them  in  the 
luminous  flame  of  the  lamp  until  they  are  thoroughly  coated 
with  soot  and  then  allowing  them  to  stand  until  cold. 

Amateurs  that  have  difficulty  in  blowing  glass  bulbs  in  the 
middle  of  tubes  will  find  it  convenient  to  order  from  a  glass 
manufacturer  a  supply  of  thin  walled  glass  bulbs,  of  from  four 
cm.  to  seven  cm.  in  diameter,  with  side  tubes  of  from  seven  mm. 
to  twelve  mm.  external  diameter  and  each  about  fifteen  cm.  long. 

"3 


114  GAS   ANALYSIS 

Since  some  find  difficulty  in  properly  bending  capillary  tub- 
ing for  the  Hempel  apparatus  it  may  be  stated  that  such  tubing, 
which  should  be  six  mm.  external  diameter  with  one  mm.  bore, 
may  easily  be  bent,  without  blowing,  by  first  warming  it  care- 
fully in  the  luminous  flame  of  the  blast  lamp,  and  then  heating 
the  spot  at  which  the  bend  is  to  be  made  in  a  blast  flame 
about  two  cm.  wide,  turning  the  tubing  during  the  heating. 
As  soon  as  the  tube  softens,  it  is  bent  directly  to  the  desired 
angle  as  one  would  bend  a  piece  of  glass  rod. 

Mounting  of  Apparatus. — If  glass  apparatus  is  to  be  mounted 
on  a  frame  or  standard,  it  should  be  fastened  at  only  a  few 
places  so  as  to  allow  of  as  free  expansion  as  possible,  and  it  is 
best  secured  in  position  by  fastening  to  the  support  a  metal  band 
that  passes  around  the  glass  tube,  but  does  not  touch  it,  and 
then  filling  the  intervening  space  between  the  metal  strap  and 
the  tube  with  Plaster  of  Paris. 

Rubber  Connections.  —  If  glass  tubes  are  to  be  joined  to- 
gether by  rubber  tubing,  the  ends  of  the  tubes  should  be  rounded 
in  the  flame,  and  should  be  brought  close  together  within  the 
piece  of  rubber  tubing.  To  secure  the  rubber  tubing  in  place, 
it  may  be  fastened  by  wire  ligatures.  For  this  purpose  copper 
wire  about  one  mm.  in  diameter  is  most  suitable.  Each  ligature 
should  consist  of  only  one  turn  of  the  copper  wire  around  the 
tube,  the  ends  being  drawn  and  tightly  twisted  together  by 
means  of  a  pair  of  pliers.  Long  rubber  connections  should  be 
avoided,  not  merely  because  the  rubber  tubing  is  somewhat  por- 
ous, but  also  because  air  in  the  tube  adheres  tenaciously  to  the 
walls.  A  rubber  tube  capable  of  withstanding  high  pressure  is 
needed  in  connecting  level-tubes  or  level-bulbs  with  gas  burettes 
when  the  apparatus  is  to  be  filled  with  mercury  as  the  confining 
liquid.  For  this  purpose  the  so-called  enamelled  rubber  tubing 
about  six  mm.  internal  diameter  and  with  a  wall  two  mm.  thick 
will  be  found  very  satisfactory.  For  connecting  the  level-bulb  of 
a  mercury  air  pump  with  the  pump,  enamelled  rubber  tubing 
about  twelve  mm.  internal  diameter  and  2.5  mm.  thickness  of 


CONSTRUCTION  AND  CONNECTION  OF  APPARATUS    115 

wall  may  be  employed.  The  enamelled  tubing  is  superior  to  the 
ordinary  pressure  rubber  tubing  with  very  thick  wall,  because 
its  larger  internal  diameter  permits  free  flow  of  the  mercury,  and 
its  smooth  interior  surface  avoids  the  fouling  of  the  mercury 
by  particles  of  the  rubber.  It  has  been  found  in  practice  that  it 
will  easily  withstand  a  working  pressure  that  rises  at  times  to 
five  atmospheres. 

Stopcocks.  —  Hollow-blown  stopcocks  are  so  perfectly  made 
that  they  may  be  employed  with  very  slight  danger  of  leakage 


FIG.  6 1  FIG.  62 

provided  they  are  properly  lubricated.  The  Greiner  &  Fried- 
richs  form  of  stopcock  of  the  form  shown  in  Fig.  61  and  Fig.  62 
is  superior  to  the  stopcock  with  straight  bore  because  it  avoids 
the  danger  of  leakage  due  to  the  channeling  of  the  barrel  of  the 
stopcock. 

Lubrication  of  Stopcocks.  —  An  excellent  preparation  for 
the  lubrication  of  glass  stopcocks  that  does  not  deteriorate  on 
keeping,  does  not  work  out  at  the  ends  of  the  key,  and  gives 
off  no  hydrocarbon  vapors  may  be  made  as  follows:  Place  in  an 
evaporating  dish  twelve  parts  of  vaseline  and  one  part  of  paraf- 
fin wax.  Heat  this  mixture  over  a  Bunsen  flame  and  maintain 
the  contents  of  the  dish  at  a  temperature  that  will  keep  the 
materials  fluid  but  will  not  cause  the  mixture  to  emit  fumes. 
Drop  in  successive  portions  of  soft,  black-rubber  clippings  and 
stir  the  mixture  after  each  addition  until  the  rubber  is  com- 
pletely dissolved.  After  about  nine  parts  by  weight  of  rubber 
has  been  added,  take  out  a  small  sample  of  the  lubricant  on 
the  end  of  a  stirring  rod,  allow  it  to  cool,  place  it  on  the  ball  of 
the  thumb,  squeeze  it  with  the  end  of  the  middle  finger  and 
then  rapidly  tap  the  finger  upon  the  thumb  at  the  point  covered 


n6  GAS  ANALYSIS 

by  the  lubricant.  If  on  this  treatment  the  lubricant  forms  light 
feathery  particles  that  float  off  in  the  air  in  fine  flocks  the  proper 
mixture  has  been  reached.  If  the  lubricant  does  not  behave 
as  described,  stir  in  more  rubber  and  test  again.  About  ten 
parts  by  weight  of  the  rubber  will  usually  be  required  for  the 
above  amounts  of  vaseline  and  paraffin. 

In  lubricating  a  glass  stopcock,  the  key  and  barrel  should 
first  carefully  be  cleaned  and  then  the  thinnest  possible  film 
of  vaseline  be  rubbed  over  the  surface  of  the  key  of  the  stopcock. 
The  lubricant  is  then  rubbed  over  the  key  which  is  next  inserted 
in  the  barrel  and  turned  around  until  the  lubricant  is  evenly 
distributed  over  the  surface. 

In  the  Cornell  laboratory,  it  has  been  found  that  a  Greiner  & 
Friedrichs  stopcock  of  the  form  shown  in  Fig.  61,  when  lubri- 
cated with  this  mixture,  will  withstand  a  pressure  of  four  atmos- 
pheres on  one  side  and  a  Torricellian  vacuum  on  the  other  for 
a  considerable  length  of  time  without  any  leakage  whatsoever. 

Another  recipe  for  a  lubricant  for  stopcocks  is  given  by  Keyes:1 
26  grams  of  paraffin  (melting  point  70°)  is  placed  in  a  dish  and 
heated  until  it  melts,  and  then  18  grams  of  pure  gutta  percha 
is  added  in  small  amounts  at  a  time,  the  temperature  of  the 
mass  being  held  at  about  150°  until  the  gutta  percha  is  dis- 
solved. 20  grams  of  a  heavy  mineral  oil  such  as  is  supplied, 
with  the  Fleuss  pumps  is  then  added  and  the  mixture  is  main- 
tained at  a  temperature  of  from  1 25°  to  130°  for  four  or  five  hours. 

If  the  gases  or  liquids  that  are  to  pass  through  the  stopcock 
are  of  such  nature  as  to  cause  them  to  attack  the  rubber  lu- 
bricant, metaphosphoric  acid  may  be  used.  The  key  and 
barrel  of  the  stopcock  are  thoroughly  cleaned  and  dried;  the 
key  is  dipped  into  phosphorus  pentoxide,  is  allowed  to  stand 
in  the  air  until  the  pentoxide  has  taken  up  sufficient  water  to 
form  metaphosphoric  acid,  and  is  then  inserted  into  the  bar- 
rel and  turned  until  the  metaphosphoric  acid  is  spread  evenly 
over  the  surface. 

1J.  Am.  Chem.  Soc.,  31  (1909),  1271, 


CHAPTER  DC 
PURIFICATION  OF  MERCURY 

Mercury  that  is  pure  will  pass  over  a  glass  surfac6  without 
adhering  to  it  or  leaving  a  deposit  upon  it.  If  the  mercury  is 
contaminated  with  other  metals  there  forms  upon  the  mercury  a 
layer  of  oxides  that  adhere  to  glass.  Commercial  mercury  fre- 
quently contains  zinc  and  lead,  and  through  use  in  the  laboratory 
it  usually  soon  becomes  contaminated  with  copper.  These  for- 
eign metals  may  be  removed  by  oxidizing  them  and  then  dissolv- 
ing their  oxides  with  an  acid  that  does  not  attack  the  mercury. 
They  may  also  be  separated  from  the  mercury  by  bringing  the 
impure  metal  into  contact  with  a  mercurous  salt  and  a  free  acid, 
which  will  remove  from  the  mercury  such  metals  as  stand  above 
it  in  the  electromotive  series,  the  foreign  metals  passing  into  the 
solution  and  precipitating  an  equivalent  amount  of  mercury. 
Metals  that  stand  below  mercury  in  the  electromotive  series, 
such  as  platinum  and  gold,  cannot  be  separated  from  the  mercury 
in  this  manner.  In  such  case  it  is  best  to  distill  the  mercury  un- 
der diminished  pressure.  It  was  formerly  supposed  that  certain 
metals,  such  as  zinc,  would  distill  over  with  the  mercury,  but 
Hulett  has  shown  1  that  this  does  not  take  place  if  bumping 
of  the  mercury  during  distillation  is  avo.ided.  He  has  ascer- 
tained, however,  that  when  the  mercury  is  contaminated  with 
dry  metallic  oxides,  these  oxides  may  be  carried  over  with  the 
mercury  vapor. 

If  the  mercury  is  very  impure  a  considerable  portion  of  the 
dirt  and  oxides  may  be  removed  by  running  the  mercury  through 
a  dry  filter  paper  that  is  folded  and  placed  in  a  glass  funnel  in 
the  usual  manner  after  the  tip  of  the  filter  has  been  cut  off. 

1  Z.  physikalische  Chemie,  33  (1900),  611. 
117 


n8 


GAS  ANALYSIS 


The  hole  in  the  end  of  the  filter  paper  should  be  from  one  to 
two  mm.  in  diameter.  The  metal  may  then  be  purified  by  one 
of  the  processes  described  below. 

Purification  of  Mercury  by  Nitric  Acid. 
—  If  the  mercury  is  highly  contaminated 
with  other  metals  it  may  rapidly  be  freed 
from  a  considerable  portion  of  these  metals 
by  placing  it  in  a  bottle,  covering  it  with  a 
layer  of  a  five  per  cent  solution  of  nitric 
acid,  and  blowing  air  through  the  mercury 
through  a  glass  tube.  If  air  blast  is  not 
available,  the  mercury  and  acid  may  be 
placed  in  a  filtering  flask  into  the  neck  of 
which  is  inserted  a  one-hole  stopper  carry- 
ing a  glass  tube  reaching  nearly  to  the  bot- 
tom of  the  flask.  Upon  connecting  the 
side  arm  of  the  flask  with  a  suction  pump, 
air  will  be  drawn  down  through  the  tube 
and  will  pass  upward  through  the  mer- 
cury. 

Further  purification  of  the  mer- 
cury by  means  of  nitric  acid  may 
then  be  effected  by  use  of  the  ap- 
paratus shown  in  Fig.  63. 

A  is  a  glass  tube  one  meter  long, 
from  2  to  3  cm.  wide,  and  fitted  at 
the  lower  end  with  a  cork  and  the 
^  bent  glass  tube  D.    B  is  the  sup- 
f  ply  bottle  for  impure  mercury,  and 
C   the   receiver    for    the    purified 
FIG.  63  mercury.     The  lower  end  of  the 

tube  from  B  is  drawn  down  to  a 

small  opening.  Some  pure  mercury  is  first  poured  into  the 
tube  D,  and  A  is  then  filled  with  5  per  cent  nitric  acid,  the 
acid  being  kept  in  the  tube  by  the  mercury  in  D.  Upon  allow- 


PURIFICATION  OF   MERCURY  119 

ing  the  mercury  to  drop  from  B,  the  purified  metal  passes 
slowly  over  into  C. 

Purification  of  Mercury  by  Concentrated  Sulphuric  Acid 
and  Mercurous  Sulphate.  —  This  is  a  very  simple  and  efficient 
method  which  yields  mercury  that  is  both  dry  and  of  high 
purity. 

The  process  of  purification  may  conveniently  be  carried  out 
in  a  heavy  separatory  funnel  of  from  2  to  4  liters  capacity,  the 
funnel  being  supported  in  a  wooden  stand  at  such  a  height  that 
an  ordinary  bottle  or  beaker  may  readily  be  brought  under 
its  lower  end.  The  funnel  is  first  partly  filled  with  mercury 
(impure  mercury  may  be  used  here,  if  no  purified  mercury  is  at 
hand),  and  then  about  500  cc.  of  concentrated  sulphuric  acid  is 
poured  upon  the  mercury  and  from  25  to  50  grams  of  mercurous 
sulphate  is  added.  In  the  top  of  the  separatory  funnel  is  placed 
an  ordinary  funnel,  the  stem  of  which  is  drawn  out  to  small 
diameter  and  turned  upward.  The  mercury  to  be  purified  is 
poured  into  this  latter  funnel  and  flows  slowly  and  in  the  form  of 
a  fine  spray  out  of  the  end  of  the  stem.  It  is  freed  from  foreign 
metals  that  stand  above  it  in  the  electromotive  series  by  the 
action  of  the  sulphuric  acid  and  mercurous  sulphate,  and 
is  thoroughly  dried  by  passing  through  the  concentrated  acid, 
so  that  pure  and  dry  mercury  may  at  any  time  be  drawn 
off  from  the  separatory  funnel.  In  starting  the  process, 
impure  mercury  which  may  first  have  been  put  into  the  funnel 
should,  of  course,  be  drawn  off  and  run  through  the  purifier  a 
second  time.  The  mercury  in  the  sepajatory  funnel  should 
never  be  drawn  down  until  it  is  near  the  stopcock,  for  some 
sulphuric  acid  might  be  drawn  off  with  it. 

Purification  of  Mercury  by  Distillation.  —  This  method, 
as  stated  above,  gives  satisfactory  results  if  the  mercury  is 
free  from  oxides  and  if  bumping  of  the  liquid  during  distilla- 
tion is  avoided.  If  foreign  oxides  are  present,  they  should  first 
be  removed  by  one  of  the  methods  described  above. 

Of  the  many  forms  of  apparatus  that  have  been  suggested 


120 


GAS   ANALYSIS 


A    0       W 


FIG.  64 


for  the  distillation  of  mercury 
that  shown  in  Fig.  64  is  one  of 
the  simplest  and  most  satis- 
factory. All  glass  parts  of  the 
device  are  of  Jena  glass.  The 
mercury  is  boiled  in  the  bulb 
A  which  has  a  diameter  of 
about  7  cm.  The  neck  of  the 
bulb  A  is  fused  to  the  outside 
of  the  tube  G  just  above  B, 
and  has  a  side  arm  K  that  is 
connected  with  the  level-bulb 
If  by  a  piece  of  enamelled  rub- 
ber tube.  To  the  lower  side 
of  the  bulb  B  is  attached  a 
tube  of  5  mm.  internal  di- 
ameter, and  15  cm.  long,  and 
to  this  is  fused  the  capillary 
tube  C  that  has  a  bore  of 
about  one  mm.  diameter,  and 
a  length  of  about  800  mm. 
The  lower  end  of  C  is  bent 
upward  and  widened  at  D, 
and  then  is  brought  up  over 
the  middle  of  the  box  and 
turned  downward  at  E. 

To  start  the  distillation,  dry 
mercury  that  has  been  freed 
from  oxides  is  poured  into  the 
level-bulb  M ,  and  the  capillary 
tube  E  is  connected  with  a 
mercury  pump  or  with  an  ef- 
ficient water  suction  pump 
if  a  mercury  pump  is  not 
available.  M  is  then  raised 


PURIFICATION   OF   MERCURY  121 

until  the  mercury  rises  in  A  nearly  to  the  top  of  the  tube  G, 
and  the  pumping  is  continued  until  all  the  air  possible  has 
been  drawn  out  of  B  through  C.  M  is  then  slipped  into  its 
adjustable  support,  and  this  is  set  at  such  a  height  in  the  slot  6" 
by  means  of  a  set  screw  that  the  bulb  A  is  about  half  filled  with 
mercury.  The  ring  burner  W  is  now  lighted  and  the  mercury 
carefully  brought  to  boiling.  The  height  of  the  level-bulb  M 
is  readjusted  so  that  the  bulb  A  stands  half  full  of  mer- 
cury. The  vapor  of  the  mercury  passes  from  A  down  through 
G  into  B,  and  escapes  through  the  open  end  of  the  capillary  E 
into  a  container  placed  below  E  to  receive  it. 


CHAPTER  X 

ABSORPTION  APPARATUS  FOR  USE  WITH  LARGE 
VOLUMES  OF  GAS 

Gases  that  are  very  soluble  in  water  or  that  are  present  in 
only  small  amount  in  a  mixture  of  gases  are  best  determined 
by  passing  the  gas  mixture  through  suitable  absorption  ap- 
paratus to  remove  these  constituents  and  then  ascertaining 
the  quantity  of  the  absorbed  gas  by  gravimetric  or  volumetric 
methods.  The  total  volume  of  the  gas  mixture  that  is  passed 
through  the  absorption  apparatus  is  measured  by  a  suitable 
device,  such  as  an  experimental  gas  meter.  The  meter  is  placed 
before  the  absorption  apparatus  if  the  gas  that  is  to  be  deter- 
mined is  not  appreciably  soluble  in  water.  Otherwise  it  is  placed 
after  the  absorbent. 

This  method  of  analysis  is  particularly  well  adapted  to  the 
determination  of  minute  amounts  of  a  gas  in  a  gas  mixture  for 
the  reason  that  the  large  size  of  the  sample  that  may  here  be 
employed  renders  the  results  very  accurate  if  the  absorbed 
constituent  is  correctly  determined.  To  illustrate  how  slight 
is  the  effect,  upon  the  final  result,  of  a  considerable  error  in  the 
measurement  of  the  sample,  let  us  suppose  that,  in  the  deter- 
mination of  carbon  dioxide  in  air,  a  sample  of  ten  liters  has  been 
passed  through  the  apparatus  and  the  titration  shows  four  cc. 
of  carbon  dioxide,  or  0.04  per  cent.  If  a  mistake  of  100  cc.  were 
made  in  the  measurement  of  the  sample,  which  would  be  a  very 
large  experimental  error,  the  result  calculated  for  10100  cc.  would 
be  0.0396  per  cent  carbon  dioxide,  and  for  9900  cc.,  0.0404  per 
cent.  To  obtain  the  same  accuracy  by  the  volumetric  analysis 
of  a  sample  of  air  measuring  100  cc.  the  readings  would  have 
to  be  correct  to  the  hundredth  of  a  cubic  centimeter. 

122 


ABSORPTION  APPARATUS 


123 


To  effect  the  complete  absorption  of  a  gas  by  a  liquid,  it  is 
necessary  that  the  gas  be  broken  up  into  fine  bubbles  before 
or  while  passing  through  the  absorbent,  or  that  it  remain  in 
contact  with  the  liquid  for  a  considerable  length  of  time.  The 
former  procedure,  being  more  rapid,  is  usually  to  be  preferred, 
and  in  the  most  efficient  forms  of  absorption  apparatus  the  gas 
enters  the  absorbent  through  small  orifices  in  the  inlet  tube,  or 
passes  upward  through  a  column  of  glass 
beads  or  of  pieces  of  broken  glass  that  are 
moistened  with  the  absorbent.  Many 
forms  of  the  first  type  of  absorption  ap- 
paratus have  been  described  and  most  of 
them  are  doubtless  familiar  to  the  reader. 
Special  forms  of  such  apparatus  are  pic- 
tured on  pages  228  and  359. 

A  novel  form  of  gas  washing  bottle  that 
has  been  thoroughly  tested  in  the  Cornell 
laboratory  and  found  to  be  very  efficient 
is  shown  in  Fig.  65.  It  is  a  slight  mod- 
ification of  the  spiral  gas  washing  bottle 
recently  designed  by  Fritz  Friedrichs  and 
placed  upon  the  market  by  Greiner  and 
Friedrichs.  In  preparing  the  bottle  for 
use  the  stopper  with  the  attached  inner 
cylinder  is  removed,  and  the  absorbing 
liquid  is  introduced  into  the  outer  cylinder 
in  such  amount  that  when  the  inner  cyl- 1 
inder  is  replaced  the  liquid  will  stand  at 
the  height  of  the  lowest  spiral.  The  gas  enters  the  bottle  at  A 
and  passes  into  the  absorbing  liquid  through  small  openings  in 
the  bottom  of  the  inner  cylinder.  It  cannot  escape  directly  up- 
ward, but  must  pass  around  the  spirals,  which  it  does  in  the 
form  of  a  procession  of  gas  bubbles  that  push  ahead  of  them 
small  amounts  of  the  absorbing  liquid.  The  contact  between 
the  gas  and  the  absorbent  is  intimate  and  of  considerable 


FIG.  65 


124 


GAS  ANALYSIS 


duration,  and  the  consequent  absorption  is  very  complete. 
This  form  of  the  bottle  was  particularly  designed  for  quantitative 
work.  Upon  removal  of  the  small  rubber  stopper  that  is  in- 
serted in  A  the  absorbing  liquid  in  the  bottle  can  easily  be 
removed,  and  the  bottle  be  thoroughly  rinsed  out.  If,  how- 
ever, the  nature  of  the  work  is  such  as  to  render  undesirable 
the  use  of  a  rubber  stopper  in  A,  the  tube  A  may  be  made 
somewhat  longer  and  bent  at  a  right  angle,  Fig.  66,  which  will 
permit  of  a  glass-to-glass  connection  of  the  apparatus. 

If  it  is  desired  merely  to  remove  a  gas 
from  a  gas  mixture,  but  not  afterward  to 
determine  its  amount,  the  apparatus  de- 
vised by  Winkler  may  be  used.  The  de- 
vice, Fig.  67,  consists  of  a  Wolff  bottle  b 
into  one  neck  of  which  is  inserted  the 
stem  of  the  cylinder  a.  To  obtain  large 
surface  of  contact  between  the  absorbent 
and  the  gas,  a  is  filled  with  pieces  of 
pumice-stone.  The  gas  enters  through 
the  tube  c  which  .extends  downward  to 
the  bottom  of  the  largest  cylindrical 
portion  of  a.  It  then  rises  through  the 
moistened  pumice-stone  and  passes  out 
through  the  tube  e.  The  bottle  b  con- 
tains the  absorbing  liquid  which  can  be 
driven  up  into  a  from  time  to  time  by 
blowing  into  the  glass  tube  d,  the  excess 

of  absorbent  immediately  flowing  back  into  b  when  the  pressure 
at  d  is  released. 

In  this  Winkler  absorption  apparatus,  however,  the  gas  that 
rises  through  the  cylinder  a  comes  in  contact  with  only  such 
portion  of  the  absorbent  as  adheres  to  the  surface  of  the  pumice- 
stone.  Moreover  if  a  large  amount  of  gas  is  being  removed  by 
the  absorbent  the  liquid  must  frequently  be  driven  up  into  a 
by  blowing  into  d.  A  modification  of  the  apparatus  that  gives 


FIG.  66 


ABSORPTION  APPARATUS 


125 


more  efficient  absorption  and  automatically  renews  the  ab- 
sorbent is  shown  in  Fig.  68.  A  Friedrichs  spiral  absorption 
tube  fits  by  a  ground  joint  into  one  neck  of  a  Wolff  bottle  that 
contains  the  solution  of  the  absorbent.  Into  the  other  neck 
of  the  Wolff  bottle  is  inserted  by  means  of  a  ground  joint  a 


FIG.  67 


FIG.  68 


short  glass  tube  T  carrying  the  stopcock  S.  Some  of  the  re- 
agent is  driven  up  into  the  absorbing  cylinder  by  opening  S 
and  blowing  into  T  whereupon  6*  is  closed.  The  gas  mixture 
enters  through  the  tube  A  and,  passing  downward  in  the  inside 
of  the  spiral,  it  enters  the  tube  B  and  passes  upward  through 
the  open  lower  end  of  the  short  tube  C.  It  then  rises 


126  GAS  ANALYSIS 

around  the  spiral  carrying  some  of  the  liquid  with  it,  and 
the  non-absorbed  gases  escape  at  D.  As  the  gas  bubbles  rise 
through  the  short  tube  C  they  draw  up  fresh  absorbent  through 
the  tube  B  and  the  absorbent  that  has  been  in  contact  with 
the  gas  flows  downward  through  the  tube  E  into  the  Wolff 
bottle  below.  In  this  manner  constant  circulation  of  the  ab- 
sorbing liquid  is  attained  and  the  apparatus  requires  no  further 
attention  after  once  it  has  been  set  in  action. 


CHAPTER  XI 
THE  COMBUSTION  OF  GASES 

Most  gases  may  quantitatively  be  removed  by  absorbents, 
and  for  this  reason  the  combustion  method  is  chiefly  employed 
for  the  determination  of  only  hydrogen,  methane  and  its  hom- 
ologues,  and  at  times  carbon  monoxide.  Under  certain  con- 
ditions, however,  it  may  be  advisable  to  determine  the  amounts 
of  other  constituents  of  a  gas  mixture  by  direct  combustion 
even  although  these  gases  may  be  absorbable  by  suitable  re- 
agents. It  is  not  always  possible  to  ascertain  from  the  results 
of  a  single  combustion  the  percentage  of  each  constituent  in 
the  gas  mixture.  De  Voldere  and  de  Smet 1  have  developed 
certain  fundamental  laws  which  show  the  possibilities  and 
limitations  of  the  combustion  method,  and  the  following  con- 
densation and  revision  of  their  original  article  has  been  pre- 
pared by  Dr.  R.  P.  Anderson. 

According  to  de  Voldere  and  de  Smet  the  gases  that  may 
accurately  be  determined  by  combustion  analysis  are  divisible 
into  three  classes: 

I.  Hydrocarbons. 

CnH2n  +  2k,  where  k  =  i,  o,  -i,  -2,  or  -3.  It  is  convenient 
to  include  under  this  head  CO,  CO2,  O2,  .and  H2  because  the 
combustion  equations  of  these  gases  are  of  the  same  type  as 
those  of  the  hydrocarbons,  as  is  evident  if  the  proper  values 
are  given  to  n  and  k.  For  example, 

if  n  =  o  and  k  =  i  CnH2n  +  2k  becomes  CoH2,  equivalent  to  H2 

"  k  =  -2      "  "       CiH-2,        "        "  CO 

"  k  =  -2      "  "       CoH-4,        "        "      O2 

=  i     "  k  =  -3      "  "       CiH_4,         "        "  CO2 

1  Die  Analyse  brennbarer  Case,  Z.f.  analyt.  Chem.,  49  (1910),  661-688. 

127 


128  GAS   ANALYSIS 

II.  Gases  containing  carbon,  hydrogen  and  oxygen. 
Formic   aldehyde,   CH2O;   methyl   ether,    (CH3)2O;  methyl 

ethyl  ether,  (CH3C2H5)O;  ethyl  ether,  (C2H5)2O;  acetaldehyde, 
C2H4O. 

III.  Gases  containing  nitrogen. 

Nitrogen,  N2;  nitrous  oxide,  N2O;  ammonia,  NH3;  hydrogen 
cyanide,  HCN. 

Other  combustible  gases  such  as  the  hydrides  of  the  fifth  and 
sixth  groups  of  the  Mendeleeff  periodic  arrangement,  halogen 
and  sulphur  hydrocarbon  substitution  products,  and  gaseous 
compounds  of  nitrogen  other  than  those  given  above,  yield 
combustion  products  that  are  not  suited  to  gas-volumetric  de- 
termination. The  following  discussion  is  confined  to  combina- 
tions of  gases  of  the  first  class,  finally  amplified  to  include  ni- 
trogen or  one  of  the  other  nitrogen-containing  gases.  For 
details  concerning  the  combustion  of  gas  mixtures  containing 
members  of  all  three  of  the  above  classes,  the  reader  is  referred 
to  the  original  article* 

In  the  combustion  of  a  hydrocarbon  four  factors  are  deter- 
minable.  These  factors  together  with  the  symbols  that  will 
here  be  used  to  represent  them  are  as  follows : 

V,  the  total  volume  of  gas  to  be  burned; 

O2,  the  volume  of  oxygen  necessary  for  the  complete  com- 
bustion of  the  gas; 

CO2,  the  volume  of  carbon  dioxide  that  is  formed  in  the  com- 
bustion; 

T.  C.,  the  total  contraction  in  volume  that  results  from  the 
combustion. 

This  total  contraction  is  equal  to  the  sum  of  the  volume 
of  the  hydrocarbon  and  of  that  of  the  oxygen  used,  less 
the  volume  of  carbon  dioxide  that  is  formed.  The  water 
that  is  produced  in  the  combustion  condenses  to  the  liquid 
state. 

T.  C.   =  V  +  02  -  CO2.  (i) 


THE   COMBUSTION   OF   GASES 


129 


The  complete  combustion  of  a  hydrocarbon,  CnH2n   +  2k, 
may  be  expressed  by  the  equation  — 


CnH2n  +  2k+ 


In  this  case: 


O2  =  nCO2  +  (n  +  k)  H2O. 


CO2  =  nV 
T.c.    =2 


(2) 

(3) 
(4) 


The  following  table  gives  the  values  of  O2,  CO2,  and  T.  C. 
per  unit  volume  of  hydrocarbons  of  the  various  groups. 

TABLE  I 


Jj. 

GROUP 

02 

C02 

T.C. 

EXAMPLES 

I 

o 

CnH2n  +  2k 
CnH2n 

fntT    -n 

3n  +  i 

n 
n 
n 
n 
n 

n  +  3 

CH4C2H6,C3H8,H2 
C2H4 
C2H2 
C0,02 
CO2 

2 

3" 

2 

n  +  2 

2 

3n-  i 

2 

n+  i 

—  I 

CnH2n  -  4 
CnH2n  -  6 

2 

3n-2 

2 

n 

2 

n  —  i 

2 

3n-3 

3 

2 

2 

The  four  factors,  V,  O2,  CO2,  and  T.  C.  can  also  be  determined 
in  the  combustion  of  any  mixture  of  hydrocarbons,  and  by  means 
of  equations  expressing  the  relationships  between  these  four 
factors  and  the  unknown  volumes  of  the  gases  that  are  present, 
the  volumes  can,  in  certain  cases,  be  computed.  A  study  of  these 


130  GAS  ANALYSIS 

equations  shows  that  the  number  of  gases  that  can  be  determined 
depends  upon  the  nature  of  the  gas  mixture.  The  different  pos- 
sibilities are  discussed  under  the  following  cases: 

FIRST  CASE.  It  is  possible,  by  means  of  one  complete  com- 
bustion, to  determine  the  percentage  composition  of  a  gas  mix- 
ture that  contains  not  more  than  two  hydrocarbons  of  the  same 
group,  provided  the  formula  of  each  constituent  is  known. 

If  a  gas  mixture  were  to  contain  several  gases  of  one  group, 
say  Group  I,  the  equations  between  the  knowns  and  unknowns 
would  be  derived  as  follows: 

Let  x,  y,  z,  .  .  .    =  volumes  of  the  gases  present 
and  n,  n',  n"  .  .  .    =  indices  of  gases  x,  y,  z  .  .  . 

Then  (from  Table  I), 

V=x+y+z+.      ..  (5) 

02     .3JL±lx+35l±Iy+3n^Mz  +        (6) 

222 

CO2  =    nx  +  n'y  +  n"z  +  .      .      .  (7) 


T.C. 


These  four  equations  are  not  independent  as  can  be  shown 
by  the  following  eliminations  : 

2O2  -  V  -  3  CO2  =0(2  xEqn.  6  -  Eqn.  5  -  3xEqn.  7)     .  (9) 
2  T.  C.  -  CO2  -  3  V  =  o  (2  xEqn.  8  -  Eqn.  7-  3xEqn.  5)  .  (10) 

Equations  9  and  10  represent  the  peculiar  relations  that 
exist  between  the  four  determinable  factors  when  the  gases  be- 
long to  the  same  group,  and  this  relation  is  such  that  the  de- 
termination of  any  two  of  these  factors  enables  one  to  compute 
the  other  two;  hence  there  are  in  reality  only  two  independent 
equations,  and  not  more  than  two  gases  of  this  group  could  be 


THE   COMBUSTION  OF   GASES 


determined  by  a  single  combustion.  Similar  relations  hold 
true  for  the  other  groups  and  the  analogous  equations  are 
given  in  the  following  table: 

TABLE  II 


GROUP 


EQUATIONS 


CnH2n  -j~2 

2  T.  C.  —  C02 

v       3  CO2  —  2  O2 

3 

—  i 

CnH2n 

2  T.  C.  —  CO2 

„       3  CO2  —  2  O2 

— 

2 

0 

or      3  CO2  =  2  O2 

CnH2n-2 

V  = 

2  T.  C.  —  CO2 

V  =  3  C02  —  2  02 

2  T.  C.  —  CO2 

3  C02  —  2  02 

o 

2 

or 

2  T.  C.  =  CO2 

V  — 

2  T.  C.  —  C02 

„  _  3  CO2  —  2  O2 

CnH2n       , 

—  i 

It  is  apparent  also  that  the  formulas  of  the  individual  gases 
are  necessary,  since  otherwise  two  new  unknowns,  n  and  n', 
would  be  introduced  and  the  number  of  unknowns  would 
exceed  the  number  of  independent  equations. 

A  gas  mixture  that  rather  frequently  occurs  in  technical 
practice  is  one  containing  hydrogen,  methane  and  ethane. 
These  three  gases  are  hydrocarbons  of  the  same  group  under 
the  classification  that  is  here  employed,  and  since  they  belong 
to  the  same  group,  they  cannot  be  determined  by  a  single  com- 
bustion. //,  in  the  analysis  of  this  gas  mixture,  the  results  of  the 
combustion  are  computed  for  hydrogen  and  methane  alone,  the 
•volume  of  methane  will  be  too  large  by  twice  the  volume  of  the  ethane 
that  is  actually  present,  and  the  volume  of  hydrogen  will  be  too 
small  by  a  volume  equal  to  that  of  the  ethane  that  is  present,  en- 
tirely independent  of  the  relative  percentages  of  each. 


132  GAS  ANALYSIS 

The  following  calculation  will  make  this  clear: 

Let  H2,  CH4  and  C2H6  represent  the  volumes  of  hydrogen. 

methane,  and  ethane  in  a  mixture  of  these  three  gases. 

Then,  giving  the  proper  values  to  n,  n/  and  n"  in  equations 

7  and  8, 

T.  C.  =  |  H2  +  2  CH4  +  ^  C2H6  (n) 

and  CO2  =  CH4  +  2  C2H6  (12) 

Now,  let  x  and  y  represent  the  amounts  of  hydrogen  and 
methane  obtained  when  the  computation  is  based  upon  these 
two  gases. 

Then  T.  C.  =  |  x  +  2  y  (13) 

And  CO2      =  y  (14) 

|x  +2y  =^H2+ 2CH4+fc2H6(Eqn.  n—  Eqn.  13)  (15) 

y  =  CH4  +  2  C2H6  (Eqn.  12  —  Eqn.  14)  (16) 

x  =     H2  C2H6(-[Eqn.i5— 2xEqn.i6])(i7) 

o 

For  example,  if  a  gas  mixture  contains  equal  volumes  of 
hydrogen,  methane,  and  ethane,  and  the  combustion  data  are 
computed  for  hydrogen  and  methane  alone,  the  result  would 
indicate  that  the  gas  mixture  contains  only  methane  (see 
Equations  16  and  17). 

In  the  analysis  of  such  gas  mixtures  as  coal  gas,  producer 
gas,  or  water  gas  the  residue  after  the  removal  of  the  absorb- 
able  constituents  is  frequently  assumed  to  consist  of  hydrogen, 
methane  and  nitrogen,  and  a  calculation  of  the  combustion 
results  is  based  upon  this  assumption.  It  is  clear  from  what 
has  been  stated  above  that  this  assumption  may  lead  to  errors 
of  considerable  magnitude  in  the  percentages  of  hydrogen  and 
methane  if  ethane  is  present.  The  percentage  of  nitrogen, 
however,  is  not  affected,  since  the  sum  of  the  percentages  of 


THE   COMBUSTION  OF  GASES  133 

hydrogen  and  methane  apparently  present  is  equal  to  the  sum 
of  the  percentages  of  hydrogen,  methane  and  ethane  actually 
present. 

SECOND  CASE.  It  is  possible,  by  means  of  one  complete 
combustion,  to  determine  the  percentage  composition  of  a  gas 
mixture  that  contains  not  more  than  three  hydrocarbons,  two 
of  them  of  the  same  group,  provided  the  formula  of  each  con- 
stituent is  known. 

If  a  gas  mixture  of  this  type  were  to  contain  two  gases  of 
Group  I  and  one  gas  of  each  of  the  remaining  groups,  the  equa- 
tions would  be  derived  as  follows : 

Let  x,  y,  z,  .  .  .  =  volumes  of  the  two  gases  of  Group  I 
and  the  gases  from  the  other  groups  respectively,  and  n,  n',  n", 
.  .  .  =  indices  of  gases  x,  y,  z,  etc. 

Then, 

V         =  x  -f  y  +  z  +  .     .     .  (1.8) 


2  22 

CO2     =  nx  -f  n'y  +  n"z  +    .     .     .  (20) 

T  C        n  +3x  4-  n/  +  3v  -f  n"  +  2Z  +  (2I) 

A.  \s.     =    ~              a>   T"                     jf      '                        *   ^r  . -•  •        •          \^ A  / 


But  inasmuch  as 
V  +  O2  =  CO2  +  T.  C.  (see  Equation  i)     .      .      .      (22) 

holds  true  for  the  combustion  of  any  mixture  of  hydrocarbons, 
it  is  clear  that  if  three  of  the  four  factors,  V,  O2,  CO2,  and  T.  C., 
are  known,  the  fourth  may  be  computed.  From  this  it  follows 
that  there  are  really  only  three  independent  equations,  and  for 
this  reason  more  than  three  hydrocarbons,  two  of  them  of  the 
same  group,  cannot  be  determined  by  a  single  combustion. 
Moreover,  as  was  shown  under  First  Case,  the  formula  of  each 
gas  must  be  known. 


134  '  GAS  ANALYSIS 

THIRD  CASE.  It  is  usually  possible  by  means  of  one  com- 
plete combustion  to  determine  the  percentage  composition  of 
a  gas  mixture  that  contains  not  more  than  three  hydrocarbons, 
all  of  them  of  different  groups,  provided  the  formula  of  each 
constituent  is  known. 

If  a  gas  mixture  of  this  type  were  to  contain  one  gas  from 
each  group,  the  equations  would  be  derived  as  follows: 
Let  x,  y,  z,  .  .  .    =  volumes  of  gases  of  ist,  2d,  3d  ...  groups 
And  n,  n',  n"  .  .  .    =  indices  of  gases,  x,  y,  z  .  .  .  etc. 

Then 

V       =  x  +  y  +  z  -f   .    .    .  (23) 

311  +  i          3n'          3n" —  i  ,    . 

02     =  — —  x+^-y+^ z+ .   .   .     (24) 

222 

CO2  =  nx  +  n'y  +  n"z  -f   .    .    .  (25) 

T.C.=     ^x+^y+^±_'z+   ...    (26) 

222 

For  the  same  reasons  as  those  given  under  Second  Case,  not 
more  than  three  hydrocarbons  belonging  to  different  groups  can 
be  determined,  and  the  formula  of  each  must  be  known.  But 
in  mixtures  that  would  be  classed  under  the  Third  Case  there 
may  exist  a  peculiar  relation  between  the  indices  of  the  various 
gases  that  will  render  the  equations  indeterminate.  For  ex- 
ample, if  a  gas  mixture  contains  one  gas  from  each  of  the  fol- 
lowing groups,  CnH2n+2,  CnH2n_4,  and  CnH2n_-6,  then 

V         =    x   +  y  +  z  (27) 

2  O2    =  (3n  +  i)x  +  fen'  —  2)y  +  (3n"  —  3)z  (28) 
2T.C.  =  (n  +  3)x  +  n'y  +  (n"  —  i)z  (29) 

CO2     =  nx  +  n'y  +  n/rz  (30) 

Solving  for  x  (or  y  or  z), 

(4n'  —  3n"  —  n)x  =  some  expression  in  terms  of  V,  O2, 
T.  C.,  andCO2.  (31) 


THE   COMBUSTION  OF   GASES 


135 


When  the  relation  between  n,  n'  and  n"  is  such  that 
4  n'  —  3  n"  —  n  =  o,  or  n'  = ,  the  equation  is  inde- 


terminate. This  is  true  when  n  =  n7  =  n"  =  i,  as  for  example 
when  the  gas  mixture  contains  methane,  carbon  monoxide,  and 
carbon  dioxide. 

Since  the  gases  classified  under  the  Third  Case  may  belong 
to  any  one  of  five  groups  (see  p.  129)  there  are  ten  possible 
combinations  under  this  case. 

If  the  five  groups  are  represented  by  A,  B,  C,  D,  E,  and  the 
indices  of  the  three  gases  in  the  mixture  are  represented  by 
n,  n'  and  n"  in  the  order  of  the  groups,  then  the  determinants 
and  the  indeterminate  examples  among  the  gases  in  Table  I 
may  be  tabulated  as  follows: 


TABLE  III 


COMBINATION 


DETERMINANT 


INDETERMINATE  EXAMPLES 


ABC. 
BCD. 
CDE  . 
ACE  . 

ABD  . 
BCE  . 

A  CD  . 
BDE  . 


ABE    . 
ADE    . 


j       n"  +  n 


j       m"  +  n 


C2H6,  C2H4, 

C3H8,  C2H2,  C02 
C3H8,  C2H4,  02 


'  CH4,  CO,  C02 


136  GAS   ANALYSIS 

FOURTH  CASE.  When  a  gas  mixture  contains  hydrocar- 
bons that  belong  to  not  more  than  two  groups,  the  percentage 
of  each  group  in  the  mixture  may  be  determined  by  means  of 
one  complete  combustion  if  the  general  formula  of  each  group 
is  known. 

Let  V  be  a  mixture  of  two  groups,  of  volumes  X  and  Y  to  be 
determined,  each  a  mixture  of  several  gases  xi,  X2,  x3,  .  .  .  and 

yi,  72,  ys,  .  .  . 

Also  let  HI,  n2,  n3,  .  .  .  and  n'i,  n'2,  n'3,  ...  be  the  indices  of 
the  gases,  and  k  and  k/  the  constants  of  the  two  groups. 

Then  V  =  xi  +  x2  +  x3  .  .  .  +  yi  +y2  +y3  .  .  .     (32) 

CO2  =  ni  xi  +  n2  x2  +  n3  x3  .  .  .    -f  n'i  yi  +  n'2  y2  +  n'3  ys 

...    •      (33) 

2  T.  C.      =  (m  +  k  +  2)  xi  +  (n2  +  k  +  2)  x2    .  . 
+  (n'i  +  k'  +  2)71  +  (n'2  +  k'  +  2)y2.    .    .    (34) 

2  O2  =  (3m  +  k)  xi  +  (3n2  +  k)  x2  .  .  .  +  (3n'i  +  k')  yi 
+  3n'2  +  k')y2    •    •    •  (35) 

2  T.  C.  —  2  V  —  2  =CO  k(xi  +  x2  +  x3  .   .   .  )  +  k'(yi 
+  y2  +  y3  .  .  .  )  .   .   .  (36) 

(Eqn.  34  —  2  Eqn.  32  —  Eqn.  33) 

2  T.  C.  —  2  V  —  C02  =  kX  +  k'Y  (Simplifying  Eqn.  36) 

(37) 
V  =  X  +  Y  (Simplifying  Eqn.  32)  .    .    ^    .         (38) 

From  equations  37  and  38  the  values  of  X  and  Y  can  be  de- 
termined when  k  and  k'  are  known. 

Gaseous  Hydrocarbons  and  Nitrogen 

If  nitrogen  is  present  with  the  gaseous  hydrocarbons,  the 
total  contraction  on  combustion  (see  p.  128)  is  equal  to  the  sum 
of  the  volume  of  the  mixture  and  the  volume  of  the  necessary 


THE   COMBUSTION  OF   GASES  137 

oxygen,  less  the  sum  of  the  volume  of  carbon  dioxide  formed 
and  the  volume  of  nitrogen  present,  or 

T.  C.  =  V  +  02  —  C02  -  N2  .     >     ..'  ,     .     (39) 

where  N2  represents  the  volume  of  nitrogen  in  the  gas  mixture. 
The  introduction  of  the  unknown,  N2,  in  the  preceding  equa- 
tion renders  the  four  equations  between  the  four  determinable 
factors  and  the  unknowns  independent  when  the  hydrocar- 
bons are  not  all  of  the  same  group  (Second  and  Third  Cases) 
and  gives  three  independent  equations  when  the  hydrocarbons 
are  all  of  the  same  group  (First  Case).  Thus  it  is  seen  that  the 
presence  of  nitrogen  in  a  mixture  that  is  otherwise  composed 
entirely  of  hydrocarbons  increases  the  number  of  independent 
equations  by  one  and  thereby  provides  for  its  own  determina- 
tion. In  general,  the  determinability  of  any  hydrocarbon  mix- 
ture is  not  affected  by  the  presence  of  an  unknown  amount  of 
nitrogen. 

This  also  holds  true  if  the  nitrogen  be  replaced  by  ammonia, 
or  nitrous  oxide,  or  hydrogen  cyanide,  if  the  necessary  changes 
are  made  in  the  expressions  involving  0%,  CO2,  and  T.  C. 

Summary 

1.  More  than  three  gaseous  hydrocarbons  cannot  be  deter- 
mined by  one  complete  combustion. 

2.  Two  gaseous  hydrocarbons  of  known  composition  and  of 
the  same  group  can  always  be  determined  by  one  complete 
combustion. 

3.  Three  gaseous  hydrocarbons  of  known  composition,  two 
of  which  belong  to  the  same  group,  can  always  be  determined 
by  one  complete  combustion. 

4.  Three  gaseous  hydrocarbons  of  known  composition,  but 
which  belong  to  different  groups,  can  usually  be  determined  by 
one  complete  combustion  (note  exceptions). 

5.  In  a  mixture  of  hydrocarbons  of  two  groups,  the  percent- 


138  GAS  ANALYSIS 

age  of  each  group  can  be  determined  by  one  complete  combus- 
tion. 

6.  Any  of  the  mixtures  that  have  been  mentioned  above  is 
still  determinable  even  if  an  unknown  quantity  of  nitrogen 
is  present. 

IDENTIFICATION   OF   GASEOUS   HYDROCARBONS 

To  identify  a  gaseous  hydrocarbon  or  to  determine  the  rel- 
ative amounts  of  carbon  and  hydrogen  in  a  mixture  of  hydro- 
carbons, it  is  necessary  only  to  burn  a  measured  volume  of  the 
gas  with  oxygen  and  to  determine  the  total  contraction  and  the 
carbon  dioxide  formed.  From  these  data  the  calculation  may 
be  made  as  follows: 

CnHm  +  (n  +  -)  O2  =  nCO2  +  ™  H2O 
and  if  V  =  the  volume  of  the  gas  sample 

V  CnHm  +  V  (n  +  -)  O2  =  V  nCO2  4-  V  ™-  H2O     . 

4  2 

Since  the  total  contraction,  T.  C.  =  V  +  O2  —  CO2  (see 
p.  1 28)  then,  in  the  present  case, 

T.  C.  =  V  +  Vn  +  Vm  —  Vn    or 
4 

T.  C.  =  V  +  V-    and 

4 

4  (T.  C.  -  V) 


m 


V 

Since  CO2  =  Vn 
C02 

^T 

In  the  determination  of  inflammable  gases  by  combus- 
tion over  mercury,  it  should  be  borne  in  mind  that,  if  great  ac- 
curacy is  desired,  correction  must  be  introduced  for  the  varia- 


THE   COMBUSTION  OF  GASES  139 

tion  of  the  actual  molecular  volumes  of  certain  gases  from  the 
molecular  volumes  calculated  for  these  gases  on  the  basis  of 
Avogadro's  hypothesis.  The  gram-molecular  volume  of  a  gas, 
that  is,  the  volume,  under  standard  conditions,  occupied  by 
the  molecular  weight  of  a  gas  in  grams,  is  nearly  the  same  in 
all  cases,  namely  22.4  liters.  Yet  the  gases  with  which  we 
chiefly  have  to  do  in  combustion  analysis  show  slight  variations 
from  this  mean,  and  in  one  case,  that  of  carbon  dioxide,  the  dif- 
ference is  considerable. 


M 

DH20  =  I 

M 
D 

Mol.-VoI. 
Oxygen  =  i 

H2 

2.016 

o  .  00008988     , 

22.43 

I  .0017 

02 

32.00 

O.OOI429I 

22.39 

I  .0000 

CO 

28  .  003 

O.OOI2507 

22.39 

I  .  OOOO 

CH4 

16.035 

0.0071464 

22.44 

I  .0020 

C02 

44.003 

O.OOI977 

22.  26 

0-99393 

In  the  gas  volumetric  comparison  of  hydrogen,  oxygen,  carbon 
monoxide  and  methane,  the  variations  from  one  another  do  not 
amount  to  more  than  0.2  per  cent  as  will  be  seen  from  the  figures 
in  the  last  column  of  the  table,  where  the  molecular  volumes 
are  calculated  on  the  basis  of  that  of  oxygen  as  unity.  But,  as 
Wohl  has  pointed  out,1  when  gases  that  contain  carbon  are 
burned,  an  error  too  great  to  be  disregarded  in  exact  work  will 
result  if  correction  is  not  introduced  for  the  low  molecular  vol- 
ume of  carbon  dioxide.  The  molecular  volume  of  CO2  is  99.4 
per  cent  that  of  CO.  Consequently  when  CO  is  burned,  the  gas 
volume  changes  are  accurately  represented  not  by  the  usual 
equation 

2  CO  +  O2  =  2  CO2 

2    VOl.    I   VOl.    2  VOl. 

but  by  the  following: 

2  CO  +  O2  =  2  CO2 

2  VOl.   I  VOl.   2  X  .994    =    1.988  VOl. 
1  Ber.  d.  deutsch.  chem.  Ges.,  37  (1904),  429. 


140  GAS  ANALYSIS 

If  then  the  CO  is  calculated  directly  from  the  contraction,  the 
result  will  be  1.2  per  cent  of  the  true  volume  of  CO  too  high. 
Similarly  if  the  CO  is  determined  by  absorption  of  the  CO2 
formed,  the  result  will  be  0.6  per  cent  of  the  true  volume  of  CO 
too  low.  For  further  details  and  for  the  statement  of  the  slight 
corrections  to  be  introduced  in  the  determination  of  H2  and  CH4 
by  combustion,  the  reader  is  referred  to  the  article  by  Wohl.1 

1  Loc.  dt. 


CHAPTER  XII 
THE   DETERMINATION    OF    GASES    BY    COMBUSTION 

ANALYSIS    BY    EXPLOSION 

The  Explosion  Pipette  for  Technical  Gas  Analysis  (Fig.  69). 
—  This  consists  of  the  thick-walled  explosion-bulb  A  and  the 
level-bulb  B,  which  are  joined  together  by  a  piece  of  enamelled 


FIG.  69 

rubber  tubing  T.  The  explosion  bulb  is  supported  by  Plaster 
of  Paris  P  as  shown  in  the  figure.  At  C  two  fine  platinum  wires 
are  fused  into  the  explosion  pipette,  the  ends  of  the  wires  being 
about  2  mm.  apart.  At  D  is  a  glass  stopcock,  and  the  pipette 
terminates  in  the  capillary  K,  whose  end  is  closed  by  a  short 
piece  of  rubber  tubing  5  and  a  stout  pinchcock. 

141 


142  GAS  ANALYSIS 

The  gas  mixture  that  is  to  be  exploded  is  introduced  into  the 
bulb  A,  the  gas  is  brought  approximately  to  atmospheric  pres- 
sure, and  the  glass  stopcock  D  is  closed.  The  rubber  tube  5  is 
next  closed  by  the  pinchcock,  and  a  piece  of  glass  rod  is  slipped 
into  the  end  of  the  rubber  tube.  The  pipette  is  then  vigorously 
shaken  to  insure  full  mixture  of  the  gases,  the  terminals  at  C  are 
connected  with  the  poles  of  an  induction  coil,  a  screen  of  plate 
glass  is  placed  in  front  of  the  pipette  and  the  current  is  turned 
on.  The  stopcock  D  is  now  opened  at  once,  and  the  gas  in  the 
pipette  is  transferred  without  delay  to  the  burette,  and  is  meas- 
ured at  once  if  the  burette  is  filled  with  mercury,  or  after  one 
minute  if  the  burette  contains  water. 

In  general,  the  pipettes  and  burettes  for  technical  gas  analysis 
are  filled  with  aqueous  solutions,  but  the  explosion  pipette  is 
filled  with  mercury.  By  using  mercury  as  confining  liquid 
during  the  explosion  it  is  possible  afterward  to  determine  the 
carbon  dioxide  formed  in  the  combustion.  If  the  explosion  is 
made  over  water,  a  subsequent  measuring  of  the  carbon  dioxide 
formed  is  inadmissible,  because  the  pressure  in  the  pipette  is 
so  high  during  the  explosion  that  considerable  quantities  of 
carbon  dioxide  are  absorbed  by  the  water.  By  exploding  over 
mercury  very  satisfactory  results  are  obtained,  even  if  the  car- 
bon dioxide  is  afterward  measured  in  a  burette  that  contains 
water  as  the  confining  liquid. 

If  the  explosion  is  too  violent  it  is  possible  that  some  oxides 
of  nitrogen  may  be  formed,  if  nitrogen  is  present.  On  the  other 
hand,  if  the  combustion  in  the  pipette  proceeds  too  slowly,  the 
oxidation  of  the  gases  is  probably  not  complete.  The  closing 
of  the  capillary  of  the  explosion  pipette  in  the  manner  above 
described  furnishes  not  only  a  sort  of  safety-valve,  for  the  re- 
lease of  pressure  if  the  explosion  is  too  violent,  but  also  affords 
means  of  judging  the  energy  of  the  explosion.  If  the  explosion 
has  the  proper  intensity,  there  will  be  a  quick  jerk  of  the  rubber 
tube  at  the  moment  of  explosion,  but  both  pinchcock  and  glass 
plug  will  remain  in  place.  With  too  violent  an  explosion,  the 


DETERMINATION   OF   GASES   BY   COMBUSTION     143 

pinchcock  is  forced  open,  and  the  glass  plug  is  driven  out  of  the 
rubber  tube.  If  the  combustion  is  not  sufficiently  vigorous,  no 
movement  of  the  rubber  tube  is  seen.  From  these  statements 
it  is  apparent  that  the  suggestion  to  modify  the  Hempel  ex- 
plosion pipette  by  placing  a  glass  stopcock  at  the  upper  end  of 
the  capillary  K,  not  merely  exposes  the  operator  to  the 
danger  of  accident  through  the  bursting  of  the  pipette,  but 
also  deprives  him  of  a  means  of  judging  the  intensity  of  the 
explosion.  . 

Proportion  of  Gases  in  Analysis  by  Explosion.  —  Bunsen 
found  that  — 

100  vol.  of  airwith  13.45  oxyhydrogen  gas  would  not  burn. 

Vol.  of  Air 
remaining 

100  air  burned  with  26.26  oxyhydrogen  gas,  left  100.02 


100  34.66 

100  "  43.72 

zoo  "  "  51.12 

loo  "  "  64.31 

ioo  "  "  78.76 

100  "  "  97.84 

ioo  "  "  226.04 


100.15 
100.07 

99.98 
99.90 

99-43 
96.92 

88.56 


These  results  led  Bunsen  to  recommend  that  in  the  determina- 
tion of  hydrogen  by  explosion  not  less  than  26  volumes  nor 
more  than  64  volumes  of  combustible  gas  be  used  to  ioo  vol- 
umes of  incombustible  gas.  It  should,  however,  be  borne  in 
mind  that  the  above  proportions  refer  only  to  the  explosion  of 
mixtures  of  hydrogen  and  oxygen.  With  combustible  gases 
other  than  hydrogen  quite  different  ratios  should  be  used.  This 
is  evidenced  by  the  results  of  Teclu1  who  finds  that  mixtures  of 
hydrogen,  methane,  acetylene  and  illuminating  gas  are  explosive 
only  when  the  amount  of  the  combustible  gas  lies  between  the 
following  percentage  volumes :  — 

1  Jour,  fur  praktische  Chemie,  75  (1907),  212.  See  also  Burrell,  /.  Ind.  Eng. 
Chem.  5  (1913),  181. 


144  GAS  ANALYSIS 

Hydrogen,  10  to  63      per  cent 
Methane,  3.5  "      7.9 
Acetylene,  1.6  "      5.8 
Illuminat- 
ing Gas  4.5  "    23.5 

Formation  of  Oxides  of  Nitrogen.  —  It  was  long  supposed 
that  if  the  explosion  of  gas  mixtures  was  made  under  the  con- 
ditions that  Bunsen  laid  down,  the  formation  of  oxides  of  ni- 
trogen would  always  be  avoided.  Experimental  evidence  now 
seems  to  show  that,  when  nitrogen  is  present,  oxides  of  nitro- 
gen are  produced  in  varying  amounts  and  that  the  quantity 
may  at  times  be  so  appreciable  as  to  introduce  a  considerable 
error  in  the  results  of  analysis.  A  further  source  of  possible 
error  in  the  determination  of  hydrogen  by  explosion  has  been 
pointed  out  by  Misteli l  who  states  that  small  amounts  of  hy- 
drogen escape  combustion. 

Induction  Coil.  —  For  producing  the  spark  for  the  explosion 
an  induction  coil  giving  a  spark  about  15  mm.  long  will  be  found 
adequate.  The  current  for  operating  this  coil  may  be  obtained 
from  either  dry  or  wet  cells  or  from  a  storage  battery  or  from 
a  dynamo  with  sufficient  resistance  in  the  circuit. 

The  Hydrogen  Pipette.  —  If  a  gas  mixture  contains  so  small 
an  amount  of  combustible  gas  that  it  will  not  explode  when 
mixed  with  oxygen  or  air,  pure  hydrogen  or  oxyhydrogen  gas 
is  added  to  the  mixture.  For  the  preparation  of  hydrogen  gas 
for  this  purpose  the  hydrogen  pipette  (Fig.  70)  may  be  used. 
This  is  a  simple  absorption  pipette  that  has  two  small  bulbs 
in  the  place  of  the  first  large  bulb.  Through  the  tube  g  a  glass 
rod  h  is  pushed  up  to  the  mouth  of  e.  This  rod  is  fastened 
tightly  into  g  by  means  of  a  piece  of  rubber  tube  slipped  over 
it,  and  it  serves  to  hold  pieces  of  chemically  pure  zinc  in  the 
bulb  e.  To  fill  the  pipette  it  is  inverted,  the  glass  rod  is  taken 
out,  and  the  pieces  of  zinc  are  dropped  into  e.  The  pipette  is 

1  Jour.fUr  Gasbdeuchtung,  48  (1905),  802. 


DETERMINATION  OF   GASES   BY   COMBUSTION    145 


then  closed  again,  placed  upright,  and  filled  with  dilute  sul- 
phuric acid  (1:10)  by  means  of  a  funnel.  The  pipette  is  closed 
at  i  with  a  piece  of  rubber  tubing  and  a  pinchcock. 

After  a  short  time  the  hydrogen  produced  will  drive  back 
the  acid,  so  that  the  evolution  ceases.  Before  drawing  off  the 
sample  of  hydrogen  from  the  pipette  it  is  advisable  to  drive  out 
the  gas  in  the  pipette  until  the 
bulb  e  is  completely  filled  with 
sulphuric  acid.  This  may  be 
done  by  blowing  into  a  rubber 
tube  attached  to  c.  A  new  sup- 
ply of  pure  hydrogen  is  now 
generated,  and  this  gas  may  be 
used  in  the  analysis.  If  several 
analyses  are  made  one  after 
another,  this  fresh  evolution  of 
the  gas  is  unnecessary;  but  if 
the  apparatus  has  stood  for  any 
length  of  time,  air  will  diffuse 
through  the  sulphuric  acid,  and 
some  oxygen  and  nitrogen  will 
be  found  in  the  first  portion  of 
hydrogen  that  is  drawn  off.  To 
obtain  a  more  active  evolution 
of  hydrogen  than  that  which 
takes  place  when  pure  zinc  and 
pure  acid  are  used,  a  few  pieces 
of  platinum  foil  may  be  put  in  with  the  zinc. 

Oxyhydrogen  Gas  Generator.  —  Oxyhydrogen  gas  may  con- 
veniently be  generated  in  the  apparatus  of  Hempel  (Fig.  71), 
which  is  patterned  after  that  described  by  Bunsen.1  It  consists 
of  a  glass  cylinder  into  which  there  is  inserted  a  cylindrical  ves- 
sel a  which  is  held  in  place  by  a  cork  fitting  into  the  neck  of 
the  outer  cylinder.  The  terminals  /  are  platinum  plates  sus- 

1  Gasometrische  Methoden,  26.  ed.  (1877),  77. 


FIG.  70 


146 


GAS  ANALYSIS 


pended  on  platinum  wires  that  are  fused  into  the  sides  of  a  and 
pass  upward  to  the  two  mercury  cups  d  and  e.  The  outer 
cylinder  is  filled  with  water  and  the  inner  cylinder  with  dilute 
sulphuric  acid  (1:10).  Into  the  neck  of  the  inner  cylinder  a 
there  is  ground  a  glass  tube  that  carries  the  bulb  c  and  ter- 
minates in  the  bent  capillary  tube  b.  In  the  generation  of 
oxyhydrogen  gas  by  the  electrolysis  of  acidulated  water  some 

ozone  is  always  formed  and  this 
gas  on  being  brought  into  the 
explosion  pipette  would  unite  with 
the  mercury.  This  would  cause  a 
small  excess  of  hydrogen  in  the 
oxyhydrogen  gas.  The  ozone  that 
is  formed  during  the  electrolysis 
may  be  converted  into  oxygen  by 
exposing  the  oxyhydrogen  gas,  be- 
fore using  it,  to  the  action  of  dif- 
fused daylight  for  twelve  hours. 
It  is  to  hasten  this  change  that  the 
bulb  c  of  about  50  cc.  capacity  is 
placed  between  the  generator  and 
the  capillary  tube  b.  To  prepare  a 
sample  of  oxyhydrogen  gas  for  use 
in  explosion  analysis,  d  and  e  are 
connected  with  a  suitable  source  of 
current  and  oxyhydrogen  gas  is 
rapidly  generated  for  about  i}4 
hours.  A  little  mercury  is  then 
introduced  into  the  open  end  of 
b  and  the  generator  is  allowed  to  stand  in  the  light  for 
twelve  hours. 

The  Explosion  Pipette  for  the  Hempel  Apparatus  for 
Exact  Analysis  (Fig.  72).  —  In  the  exact  analysis  also  it  is  most 
convenient  to  make  the  explosions  in  a  pipette  specially  con- 
structed for  the  purpose.  This  pipette  differs  from  the  ordinary 


FIG.  71 


DETERMINATION  OF   GASES  BY  COMBUSTION 


147 


pipettes  only  in  having  a  stopcock  at  a  and  two  platinum  wires 
fused  in  at  b. 

To  burn  a  gas  mixture  in  this  apparatus,  the  gas  is  brought 
into  it  in  the  usual  manner,  the  stopcock  is  closed,  and  a  fine 
sewing  needle  is  placed  in  the  mouth  of  the  capillary  c.  Upon 
connecting  the  platinum  wires  with  an  induction  apparatus, 
the  mixture  is  exploded  by  the  spark  which  passes  when  the 
circuit  is  closed. 


FIG.  72  FIG.  73 

Hydrogen  for  use  in  explosions  in  the  Hempel  exact  analysis 
may  be  made  in  the  pipette  shown  in  Fig.  73. 

The  construction  of  this  pipette  resembles  that  of  the  hydro- 
gen pipette  shown  and  described  on  page  145. 

ANALYSIS    BY    COMBUSTION 

Combustion  with  an  Electrically  Heated  Platinum  Spiral 

The  Combustion  Pipette.  —  Coquillion  was  the  first  to  pro- 
pose the  use  of  the  glowing  platinum  spiral  in  the  determination 
of  such  gases  as  marsh-gas  and  hydrogen.  Winkler  improved 
the  form  of  the  apparatus  and  used  a  Hempel  pipette  for  solid 


148 


GAS   ANALYSIS 


and  liquid  reagents.  While  adhering  in  the  main  to  the  Winkler 
arrangement,  the  author  has  modified  the  apparatus  so  that 
mercury  may  be  used  as  the  confining  liquid.  This  permits 
of  a  much  more  accurate  determination  of  carbon  monoxide 
or  hydrocarbons  than  is  possible  over  water.  The  cylin- 
drical portion  of  a  Hempel  simple  pipette  for  solid  and 
liquid  reagents,  A,  Fig.  74,  is  fastened  to  the  stand  in  the 
usual  manner,  except  that  the  bulb  is  supported  by  a  small 


FIG.  74 

block  of  Plaster  of  Paris,  P.  In  the  neck  of  the  pipette  is  in- 
serted a  two-hole  rubber  stopper  S  through  the  openings  of  which 
glass  tubes  cc  pass  from  below  the  stopper  to  within  about 
20  mm.  of  the  top  of  the  pipette.  Inside  of  each  glass  tube  is  a 
stout  iron  wire  2.5  mm.  in  diameter  which  reaches  nearly  to  the 
top  of  the  glass  tube  and  projects  about  10  mm.  below  the  lower 
end.  To  the  lower  end  of  each  iron  wire  there  is  attached  a 
small  binding  post  and  the  connection  between  the  glass  tube 
and  the  binding  post  is  made  air-tight  by  slipping  over  the 


DETERMINATION  OF  GASES  BY  COMBUSTION    149 

ends  of  each  a  short  piece  of  rubber  tubing  R  which  is  then  se- 
curely wired  in  place.  Small  iron  screws  are  threaded  into  open- 
ings in  the  upper  ends  of  the  two  iron  wires,  and  serve  to  hold  in 
place  the  ends  of  the  platinum  spiral  W.  A  strip  of  iron  about 
one  cm.  wide  is  bent  in  the  form  of  an  S  around  the  two  glass 
tubes  about  midway  up  in  the  bulb  of  the  pipette  for  the  pur- 
pose of  holding  the  tubes  more  rigidly  in  position.  The  platinum 
spiral  that  connects  the  upper  ends  of  the  two  iron  wires  is  made 
of  platinum  wire  J^  mm.  in  diameter  which  is  bent  in  a  coil 
about  2  mm.  in  diameter  and  contains  from  20  to  30  turns. 
The  ends  of  the  platinum  wire  are  fastened  under  the  two 
small  screws  in  the  upper  ends  of  the  iron  wires.  The  two 
binding  posts  that  are  fastened  to  the  lower  ends  of  the  iron 
wires  are  connected  to  two  larger  binding  posts  M  fastened 
into  a  plate  of  hard  rubber  that  is  itself  attached  to  the  base 
of  the  iron  frame.  The  combustion  pipette  is  usually  filled  with 
mercury  which  is  introduced  through  a  small  funnel  inserted 
in  the  tube  of  the  level-bulb  B.  After  the  pipette  has  been  filled 
with  the  mercury,  the  air  that  may  be  trapped  by  the  mercury 
in  the  glass  tubes  surrounding  the  iron  wires  is  removed  by 
closing  the  capillary  tube  of  the  pipette  with  a  piece  of  rubber 
tube  and  pinchcock  and  attaching  a  water  suction  pump  to 
the  tube  of  the  level-bulb. 

When  the  pipette  is  constructed  and  is  filled  with  mercury 
in  the  manner  above  described,  the  iron  wires  passing  through 
the  glass  tubes  do  not  come  into  contact  with  the  gas  mixture 
in  the  pipette  at  any  point,  for  when  a  gas  is  passed  into  the 
pipette  the  glass  tubes  remain  filled  with  mercury  which  covers 
the  ends  of  the  iron  wires.  This  makes  it  entirely  unnecessary 
to  use  heavy  platinum  wires  in  the  place  of  the  iron  wires  as 
has  been  recommended  by  Porter  and  Ovitz.1 

Manipulation  of  the  Combustion  Pipette.  —  In  carrying 
out  a  combustion  with  this  pipette  a  measured  amount  of  oxygen 
(about  100  cc.)  is  passed  into  it  from  a  gas  burette  and  the  gas 

1  Bulletin  i,  Department  of  the  Interior,  Bureau  of  Mines,  1910,  p.  24. 


150  GAS  ANALYSIS 

to  be  burned  is  then  measured  off  in  the  burette.  Ordinarily 
the  total  unabsorbable  residue  from  a  gas  sample  of  about 
100  cc.  is  used  in  the  combustion,  but  the  volume  of  the 
sample  taken  should  be  of  such  size  that  after  combustion 
an  excess  of  oxygen  remains  in  the  pipette.  The  gas  bu- 
rette H  is  connected  with  the  combustion  pipette  by  the  usual 
bent  capillary  tube,  and  the  wires  from  the  source  of  current 
are  fastened  to  the  binding  posts  on  the  frame  of  the  pipette, 
Fig.  75.  A  small  rheostat  R  is  introduced  into  the  circuit  to  per- 
mit of  ready  control  of  the  current  flowing  through  the  platinum 
spiral  and  thus  to  enable  the  operator  to  keep  the  spiral  at  dull 
redness  throughout  the  combustion.  The  current  for  heating 
the  spiral  may  be  that  from  a  storage  battery  or  from  a  dynamo, 
or  more  conveniently  the  alternating  current  of  a  lighting  cir- 
cuit. If  the  alternating  current  is  employed,  the  connections 
may  be  made  as  shown  in  the  figure.  A  plug  carrying  two  wires 
is  screwed  into  an  ordinary  lamp  socket;  one  of  the  wires  is  con- 
nected with  the  rheostat  and  the  other  with  a  bank  of  lamps  L 
connected  in  parallel.  The  further  terminal  of  the  lamps  is 
connected  with  one  of  the  binding  posts  M  on  the  pipette,  and 
the  other  binding  post  is  connected  with  the  rheostat  R.  The 
coarser  adjustment  of  the  current  is  made  by  means  of  the  lamps 
and  the  finer  adjustment  by  means  of  the  rheostat. 

Different  gases  show  great  differences  in  heat  conductivity 
and  if  adjustment  of  the  current  were  not  easily  possible 
the  spiral  might  be  raised  to  so  high  a  temperature  during  the 
process  as  to  melt  the  platinum  wire.  For  example,  when  hy- 
drogen is  burned  in  the  pipette  by  first  introducing  that  gas 
and  then  admitting  a  mixture  of  air  and  oxygen,  a  current  that 
will  at  the  beginning  heat  the  spiral  only  to  redness  in  the  at- 
mosphere of  hydrogen  will  bring  the  platinum  wire  to  a  bright 
yellow  glow  and  will  at  times  melt  it  in  the  mixture  of  nitrogen 
and  oxygen  that  remains  after  the  hydrogen  has  been  burned. 
After  the  combustible  gas  has  been  introduced,  the  platinum 
spiral  is  kept  at  dull  redness  for  60  seconds.  The  current  is  then 


DETERMINATION  OF   GASES  BY  COMBUSTION    151 


FIG.  75 


152  GAS  ANALYSIS 

turned  off,  the  pipette  is  allowed  to  cool,  and  the  gas  residue  is 
passed  back  into  the  burette  and  measured.  Air  or  a  mixture 
of  oxygen  and  air  may  be  used  in  the  pipette  in  place  of  pure 
oxygen.  If  the  combustible  gas  contains  acetylene  or  its  homo- 
logues  it  should  be  run  into  the  pipette  very  slowly  and  under 
a  pressure  that  is  only  very  slightly  above  that  of  the  prevailing 
atmospheric  pressure.  If  this  precaution  is  not  taken,  dissocia- 
tion is  liable  to  occur  when  the  gas  comes  in  contact  with  the 
hot  spiral,  and  the  separated  carbon  would  of  course  then  escape 
combustion. 

In  most  cases  the  process  may  be  reversed  and  the  combustible 
gas  be  first  introduced  into  the  pipette,  and  oxygen  or  air  or  a 
mixture  of  the  two  then  passed  in  from  the  burette.  This  ma- 
nipulation is,  however,  not  suited  to  the  combustion  of  acety- 
lene because  the  hot  spiral  causes  decomposition  of  this  gas 
with  the  deposition  of  solid  carbon. 

The  chief  merits  of  this  method  of  combustion  are: 

(1)  The  use  of  a  large  volume  of  combustible  gas  with  con- 
sequent increase  in  the  accuracy  of  the  results; 

(2)  The  avoidance  of  explosion  by  the  gradual  addition  of 
oxygen  to  the  combustible  gas  or  of  the  combustible  gas  to 
oxygen; 

(3)  The  avoidance  of  the  formation  of  measurable  amounts 
of  the  oxides  of  nitrogen  in  the  combustion  of  gas  mixtures  that 
contain  nitrogen. 

Formation  of  Oxides  of  Nitrogen  in  Combustion  Pipette. 
—  A.  H.  White  has  described  experiments  1  that  lead  him  to 
state  that  oxides  of  nitrogen  are  formed  when  hydrogen  is  burned 
with  oxygen  and  air  in  this  pipette,  and  he  bases  this  statement 
upon  the  fact  that  he  obtained  a  reaction  for  nitrites  with 
Griess's  reagent  after  heating  air  alone  in  the  combustion  pip- 
ette, and  further  that  there  was  contraction  in  volume  when  the 
products  of  the  combustion  of  hydrogen  with  oxygen  and  air 
were  passed  into  a  pipette  containing  potassium  hydroxide. 

1  Jour.  Am.  Chem,  Soc.,  23  (1901),  476. 


DETERMINATION  OF  GASES   BY   COMBUSTION     153 

F.  H.  Rhodes  has,  at  the  request  of  the  author,  carefully  re- 
peated and  extended  the  experiments  of  White,  and  he  finds 
that  no  measurable  amount  of  oxides  of  nitrogen  is  formed  when 
the  conditions  that  were  given  in  the  original  article  of  Dennis 
and  Hopkins  1  are  followed,  and  the  platinum  spiral  is  heated 
only  to  dull  redness  during  the  combustion  and  is  kept  at  dull 
redness  for  no  longer  than  sixty  seconds  after  the  gases  have 
been  introduced  into  the  pipette.  Upon  passing  air  that  has 
been  heated  in  this  manner  in  the  pipette  through  5  cc.  of  an 
8%  solution  of  pure  sodium  hydroxide,  acidifying  this  with 
acetic  acid  and  adding  i  cc.  of  Griess's  reagent,  there  resulted 
a  color  which,  on  comparison  with  a  nitrite  solution  of  known 
strength,  showed  that  not  more  than  a  trace  of  oxides  of  nitro- 
gen was  produced  under  these  conditions.  When  the  spiral  was 
heated  tor  five  minutes  to  a  temperature  of  dull  redness  in  100  cc. 
of  air,  the  colorimetric  determination  of  the  nitrite  that  was 
formed  showed  that  the  amount  of  the  oxides  of  nitrogen  pro- 
duced did  not  in  any  case  exceed  ^-g-  of  a  cc.,  and  that  the  vol- 
ume is  usually  much  less  than  this.  When  the  temperature  of 
the  spiral  was  raised  beyond  a  dull  red  heat,  the  amount  of  the 
oxides  of  nitrogen  that  was  formed  increased  with  rise  of  tem- 
perature, but  the  total  amount  of  the  product  even  after  heat- 
ing the  air  for  five  minutes  with  the  spiral  at  a  bright  yellow 
was  not  measurable  in  a  Hempel  burette  over  mercury. 

In  the  combustion  of  hydrogen  with  a  mixture  of  oxygen 
and  air,  Rhodes  found  that  when  the  spiral  is  properly  heated, 
the  amount  of  oxides  of  nitrogen  that  was  produced  is  slightly 
higher  than  when  air  alone  is  heated,  but  that  the  volume  of 
this  product  was  in  no  case  large  enough' to  permit  of  its  volu- 
metric measurement  when  100  cc.  of  hydrogen  was  burned. 
To  ascertain  whether  an  appreciable  error  would  result  in  the 
combustion  of  hydrogen  with  a  mixture  of  air  and  oxygen  when 
the  spiral  was  highly  heated,  100  cc.  of  hydrogen  was  introduced 
into  the  pipette,  the  spiral  was  heated  to  bright  yellow,  and 
1  Jour.  Am.  Chem.  Soc.t  21  (1899),  398. 


154  GAS  ANALYSIS 

100  cc.  of  a  mixture  of  equal  volumes  of  air  and  oxygen  was 
slowly  passed  in.  The  colorimetric  determination  of  the  amount 
of  nitrite  formed  when  the  products  were  passed  into  the  so- 
dium hydroxide  showed  that  even  under  these  unusual  condi- 
tions, the  volume  of  the  oxides  of  nitrogen  that  was  formed 
was  less  than  pjir  °f  a  cc->  an  error  that  is  entirely  negligible  in 
technical  gas  analysis  when  working  with  a  gas  sample  of  100  cc. 
In  the  analysis  of  gas  mixtures  that  commonly  occur  in  techni- 
cal practice,  the  error  would  be  very  much  less  than  that  above 
cited  because  of  the  lower  percentage  of  hydrogen.  As  a  fur- 
ther check  upon  the  above  results  a  mixture  of  i  cc.  of  nitrogen 
tetroxide  and  99  cc.  of  air  was  made  in  a  Hempel  burette  over 
mercury.  99  cc.  of  this  mixture  was  then  driven  out  of  the  bu- 
rette and  the  residual  i  cc.  of  gas  was  diluted  with  a  further 
99  cc.  of  air.  This  total  gas  volume,  now  containing  o.oi  per 
cent  of  nitrogen  tetroxide,  was  passed  through  a  solution  of 
sodium  hydroxide.  The  solution  was  acidified  with  acetic  acid 
and  Griess's  reagent  was  then  added.  The  depth  of  color  of  this 
solution  was  found  to  be  much  greater  than  that  resulting  from 
a  similar  treatment  of  the  gases  produced  by  the  different  meth- 
ods of  combustion  described  above,  and  this  held  true  even 
when  the  hydrogen  was  burned  under  conditions  most  favor- 
able to  the  formation  of  oxides  of  nitrogen,  namely,  high  tem- 
perature of  the  spiral  and  slow  introduction  of  the  gas. 

Combustion  with  a  Platinum  Capillary  Tube  (Drehschmidf) 

The  determination  of  combustible  gases  by  explosion  or  by 
combustion  in  the  combustion  pipette  necessitates  the  employ- 
ment of  an  electric  current.  With  the  apparatus  devised  by 
Drehschmidt 1  the  combustible  gases  mixed  either  with  air  or 
with  pure  oxygen  may  be  burned  without  danger  of  explosion 
in  a  platinum  capillary  tube  that  is  heated  to  the  requisite 
temperature  by  means  of  a  gas  flame.  In  the  original  form 

1  Berichte  d.  deutsch.  chem.  Ges.,  21  (1888),  3242. 


DETERMINATION  OF  GASES  BY  COMBUSTION    155 

proposed  by  Drehschmidt  the  platinum  combustion  tube  was 
given  a  length  of  200  mm.  to  prevent  the  ends  of  the  tube  from 
becoming  too  warm.  Winkler  improved  the  device  by  fitting 
a  water  jacket  to  each  end  of  the  tube  which  rendered  it  possible 
to  reduce  the  platinum  tube  to  a  length  of  100  mm.  The  Winkler 
form  of  tube  is  shown  in  Fig.  76.  The  combustion  tube  P  is 
of  platinum  and  has  a  length  of  100  mm.,  an  external  diameter 


W 


FIG.  76 

of  2.5  to  3  mm.  and  an  internal  diameter  of  0.7  mm.  The  tube 
should  not  be  lap-welded  but  should  be  bored  or  drawn.  Inas- 
much as  an  explosive  gas  mixture  is  passed  through  the  tube 
from  the  gas  burette,  it  is  necessary  to  prevent  the  propaga- 
tion of  the  combustion  from  the  tube  to  the  gas  mixture  in  the 
burette.  This  is  accomplished  by  filling  the  platinum  tube 
with  fine  platinum  wires.  The  ends  of  the  combustion  tube  are 
soldered  to  copper  tubes  CC  that  have  an  external  diameter 


156  GAS  ANALYSIS 

of  about  3.5  mm.  and  an  internal  diameter  of  1.5  mm.  These 
tubes  are  bent  at  right  angles  as  shown  in  the  figure  and  their 
horizontal  portions  are  also  filled  with  fine  platinum  wires. 
The  water  jackets,  WW,  are  of  sheet  brass  and  are  about  5  cm. 
long  and  2.5  cm.  wide.  They  are  fastened  upon  the  tube  in 
such  position  that  the  junctions  of  the  platinum  and  copper 
lie  within  the  water  coolers.  Each  jacket  has  an  opening  in 
the  top  for  the  introduction  of  cold  water. 

Before  being  put  in  use  the  combustion  tube  should  be  care- 
fully tested  to  ascertain  whether  it  is  tight.  This  may  be  done 
by  connecting  a  glass  tube  about  20  cm.  long  to  one  of  the  cop- 
per tubes,  immersing  the  lower  end  of  the  glass  tube  in  mercury, 
joining  the  other  copper  tube  to  a  water  suction  pump  by 
means  of  a  piece  of  rubber  tubing  and  drawing  up  the  mercury 
in  the  glass  tube  to  a  height  of  about  10  cm.  The  rubber  tube 
is  then  closed  by  a  pinchcock.  If  the  tube  does  not  leak  the 
mercury  in  the  glass  tube  will  not  fall.  If  the  tube  is  found  to 
be  tight  at  ordinary  temperatures,  the  pinchcock  is  opened,  the 
platinum  tube  is  heated  by  a  Bunsen  flame  and  the  test  is  then 
repeated.  In  the  experience  of  the  author  the  chief  objection 
to  the  Drehschmidt  tubes  that  are  now  on  the  market  lies  in 
the  fact  that  they  begin  to  leak  after  having  been  in  use  only  a 
comparatively  short  time.  This  constitutes  a  serious  drawback 
when  the  high  cost  of  the  tube  and  the  difficulty  of  repairing 
it  in  the  laboratory  are  taken  into  consideration. 

In  carrying  out  a  combustion  with  this  apparatus  the  meas- 
ured sample  of  gas  to  be  burned  is  passed  over  into  the  simple 
gas  pipette  H,  and  an  amount  of  air  or  oxygen  that  is  surely 
sufficient  to  burn  the  combustible  constituents  of  the  gas  mixture 
is  measured  off  in  the  gas  burette.  This  is  then  passed  into 
the  pipette  and  the  pinchcock  at  the  top  of  the  pipette  is  closed. 
The  Drehschmidt  tube  is  then  placed  in  position  as  shown  in 
the  figure,  the  burette  being  of  course  filled  to  the  top  with  the 
confining  liquid.  The  platinum  combustion  tube  P  is  heated 
to  bright  redness  by  means  of  the  burner  B,  the  pinchcocks  on 


DETERMINATION  OF  GASES  BY  COMBUSTION    157 

the  pipette  and  burette  are  then  opened  and  the  gas  is  slowly 
drawn  over  into  the  burette.  Two  passages  of  the  gas  through 
the  capillary  suffice  for  complete  combustion.  The  platinum 
tube  is  then  allowed  to  cool  and  the  residual  gas  is  drawn  into 
the  burette  and  measured.  The  simple  pipette  is  now  replaced 
by  a  pipette  containing  potassium  hydroxide,  and  the  carbon 
dioxide  is  removed  and  the  gas  residue  is  again  measured.  If 
hydrogen  and  methane  are  being  simultaneously  determined, 
results  of  only  approximate  accuracy  are  obtainable  when  water 
is  used  as  the  confining  liquid  in  the  burette  and  pipette.  In 
such  case  it  is  therefore  preferable  to  use  a  pipette  with  level- 
bulb  (see  Fig.  51)  and  to  employ  mercury  as  the  confining 
liquid  in  both  the  pipette  and  the  burette. 


CHAPTER 


PROPERTIES  OF  THE  VARIOUS  GASES  AND  METHODS 
FOR  THEIR  DETERMINATION 

OXYGEN 

Properties  of  Oxygen.  —  Specific  gravity,  1.1055  *;  weight 
of  one  liter,  1.4292  gram;  critical  temperature,  —  118°;  critical 
pressure,  50  atmospheres. 

Oxygen  is  but  slightly  soluble  in  water.  One  liter  of  water 
absorbs,  from  atmospheric  air,  according  to  L.  W.  Winkler,2 
Otto  Pettersson,  and  K.  Sonden,3  at  760  mm.  pressure:  — 

at        o°  C.  10.01    cc. 

6°  C.  8.3 

"    9.18°  C.  7.9 

"14.1°    C.  7.05       « 

"  16.87°  C.  6.84 

"  23.64°  C.  5-99       " 

"  24.24°  C.  5.916      " 


and  of  pure  oxygen,  according  to  Bunsen  — 
at  20°  C.,  28.38  cc. 

One  volume  of  alcohol  absorbs,  according  to  Carius,  at  all 
temperatures  between  o°  and  24°,  0.28397  volume. 

Determination  of  Oxygen.  —  Oxygen  may  be  determined 
either  by  mixing  it  with  an  excess  of  hydrogen  and  exploding 

1  Most  of  these  figures  are  from  Landolt  and  Bernstein's  Physikalisch-chemische 
T&bellen. 

zBerichte  der  deutschen  chemiscken  Gesellschaft,  21  (1888),  2843. 
3  Ibid.,  22  (1889),  1443. 

158 


PROPERTIES  OF  THE   VARIOUS   GASES  159 

the  mixture,  or  by  passing  the  gas  into  a  combustion  pipette 
containing  an  excess  of  hydrogen,  or  by  bringing  it  into  con- 
tact with  glowing  metallic  copper,  or  by  absorption  of  the  gas. 

Determination  of  Oxygen  by  Combustion.  —  The  explosion 
analysis  may  be  carried  out  in  the  apparatus  described  on 
page  141. 

The  combustion  may  most  conveniently  be  performed  in  the 
pipette  shown  in  Fig.  74. 

In  either  of  these  methods  two  volumes  of  hydrogen  unite 
with  one  volume  of  oxygen  to  form  liquid  water.  The  volume 
of  oxygen  present  is  consequently  equal  to  */3  of  the  contraction 
of  the  gas  volume. 

The  hydrogen  needed  for  these  analyses  may  be  prepared 
in  the  hydrogen  pipette  (Fig.  70)  or  it  may  be  generated  by 
the  electrolysis  of  water  in  the  Bunsen  apparatus,1  in  which 
the  positive  pole  consists  of  a  zinc  wire  floating  in  mercury. 
In  the  determination  of  oxygen  by  explosion  with  hydrogen, 
the  oxygen  should  be  mixed  with  from  three  to  ten  times  its 
volume  of  hydrogen.  If  the  amount  of  oxygen  in  the  original 
gas  mixture  is  quite  low,  there  should  be  added,  in  addition  to 
the  hydrogen,  an  amount  of  oxyhydrogen  gas  sufficient  to  render 
the  mixture  explosive. 

Determination  of  Oxygen  with  Copper  Eudiometer.  —  Very 
accurate  determinations  of  oxygen  may  be  made  by  combus- 
tion with  copper.  U.  G.  Kreusler  has  so  improved  the  ap- 
paratus devised  by  Ph.  v.  Jolly  for  the  determination  of  oxygen 
in  the  atmosphere  that  it  is  now  one  of  the  most  exact  methods 
known.  A  so-called  copper  eudiometer,  whose  construction  is 
based  upon  his  well-known  air  thermometer,  is  used  for  the 
determination.  The  air  whose  oxygen  contents  is  to  be  deter- 
mined is  admitted  into  a  bulb  that  has  previously  been  com- 
pletely exhausted,  and  the  pressure  is  read  off  on  a  very  exact 
mercury  manometer.  The  oxygen  is  then  absorbed  by  a  copper 
spiral  that  is  heated  to  glowing  by  a  strong  electric  current; 

1  Gasometrische  Methoden,  ad  ed.  (1877),  p.  80. 


160  GAS  ANALYSIS 

the  metallic  copper  is  changed  to  cuprous  and  cupric  oxide. 
After  the  apparatus  has  become  cool,  the  remaining  nitrogen 
is  brought  to  the  initial  volume  by  changing  the  pressure, 
and  a  reading  is  taken  of  the  pressure  now  prevailing.1 
When  due  regard  is  given  to  all  the  necessary  precautions,  the 
method  is  of  the  greatest  exactness;  it  is,  however,  very  complex 
and  tedious,  and  for  this  reason  is  not  well  suited  to  the  making 
of  a  large  number  of  determinations. 

Determination  of  Oxygen  by  Absorption.  —  Oxygen  may 
rapidly  and  accurately  be  determined  by  means  of  various  ab- 
sorbents, among  the  best  of  which  are  — 

1.  A  strongly  alkaline  solution  of  pyrogallol, 

2.  Phosphorus  in  solid  form, 

3.  Phosphorus  in  solution, 

4.  Metallic  copper, 

5.  Solutions  of  ferrous  salts, 

6.  Sodium  hyposulphite, 

7.  Chromous  chloride. 

i.  Alkaline  Pyrogallol 

Hempel  prepares  the  alkaline  solution  of  pyrogallol  by  dis- 
solving 120  grams  of  potassium  hydroxide  not  purified  by  alco- 
hol in  80  cc.  of  water  and  adding  to  this  5  grams  of  pyrogallol 
dissolved  in  15  cc.  of  water.  The  two  solutions  are  brought 
together  in  a  double  absorption  pipette  (Fig.  36)  or  in  the  ap- 
paratus described  on  page  161.  Hempel  states  that  a  solution 
prepared  as  above  gives  off  no  carbon  monoxide  during  the  ab- 
sorption, or  at  most  only  such  slight  amounts  that  the  error 
thus  caused  falls  within  the  limit  of  the  error  of  the  readings. 
Benedict,2  however,  appears  to  be  of  the  opinion  that  the  re- 
agent thus  prepared  will  set  free  some  carbon  monoxide  although 

1  U.  Kreusler,  Ueber  den  Sauerstojfgehcdt  der  atmospharischen  Luft.     Landwirth- 
schaftliche  Jahrbiicher,  1885,  p.  305. 

2  The  Composition  of  the  Atmosphere,  Publication  No.  166  of  the  Carnegie  Institu- 
tion of  Washington,  1912,  p.  113. 


PROPERTIES  OF  THE  VARIOUS   GASES  161 

if 

he  gives  no  experimental  proof  that  it  does  so.  He  recommends 
that  the  absorbent  be  prepared  as  follows:  500  grams  of  stick 
potassium  hydroxide,  not  purified  by  alcohol,  is  dissolved  in 
250  cc.  of  water.  The  specific  gravity  of  the  solution  is  usually 
1.55,  but,  if  it  varies  materially  from  this  figure,  more  potas- 
sium hydroxide  or  more  water  is  added  until  the  density  of 
1.55  is  reached.  135  cc.  of  this  solution  is  added  to  a  solution 
of  15  grams  of  pyrogallol  in  15  cc.  of  distilled  water. 

The  determination  should  not  be  made  at  a  temperature 
much  below  15°,  for  the  absorption  by  alkaline  pyrogallol  is 
very  much  less  active  at  a  temperature  under  7°.  At  a  tem- 
perature of  15°  or  higher,  the  last  trace  of  oxygen  can  be  re- 
moved with  certainty  in  the  space  of  three  minutes  by  shaking 
with  the  solution  of  alkaline  pyrogallol,  while  at  lower  tempera- 
tures the  absorption  is  not  complete  after  six  minutes.  The 
analytical  absorbing  power  of  the  solution  is  from  2  to  2}^. 

If  a  large  number  of  oxygen  determinations  is  to  be  made 
by  the  "exact"  method,  the  reagent  is  kept  in  the  apparatus 
shown  in  Fig.  77.  With  this  device  a  large  quantity  of  the 
reagent  may  be  stored,  measured  off,  and  transferred  to  the 
absorption  pipettes  without  coming  in  contact  with  the  air. 

The  large  reservoir  bulb  A  ends  above  in  the  U-shaped  tube  .5, 
which  has  a  short  side-arm  at/  and  ends  in  the  h— shaped  capil- 
lary g.  To  the  lower  side  of 'the  bulb  is  attached  the  bent  tube  h, 
which  is  provided  with  a  glass  stopcock  i.  A  small  funnel  can 
be  fastened  to  the  upper  end  of  h  by  a  rubber  tube  k.  A  thin 
rubber  tube  connects  the  side-arm  /  with  the  funnel  o.  The 
ends  of  the  I —  capillary  g  are  provided  with  short  pieces  of  rub- 
ber tubing  and  with  pinchcocks.  The  apparatus  is  first  filled 
completely  with  mercury.  A  funnel  or  glass  tube  is  then  in- 
serted in  the  free  end  of  m,  the  pinchcocks  n  and  y  are  closed, 
the  stopcock  i  is  opened,  and  the  aqueous  solution  of  pyrogallol 
is  poured  into  the  funnel  attached  to  m.  The  end  k  of  the  tube  h 
is  now  connected  by  a  rubber  tube  with  a  suction  flask,  and  the 
flask  is  joined  to  an  aspirator.  Upon  opening  the  pinchcock 


l62 


GAS  ANALYSIS 


at  m  the  mercury  flows  through  h  into  the  flask,  and  the  solu- 
tion of  pyrogallol  is  drawn  into  A .  The  entrance  of  the  reagent 
can  instantly  be  stopped  by  turning  the  stopcock  i.  When  all 
of  the  pyrogallol  has  entered  the  pipette,  the  solution  of  potas- 


FIG.  77 

sium  hydroxide  is  poured  into  the  funnel  and  drawn  in  in  the 
same  manner.  The  two  solutions  in  the  apparatus  are  then 
thoroughly  mixed  by  shaking. 

To  transfer  some  of  the  reagent  to  a  pipette,  the  apparatus 
is  arranged  as  shown  in  Fig.  77.    The  capillary  of  the  pipette 


PROPERTIES  OF  THE  VARIOUS   GASES  163 

is  inserted  at  y  into  the  end  of  the  rubber  tube  attached  to  the 
lower  end  of  g.  By  blowing  into  I  (this  can  best  be  done  with  the 
rubber  pump,  Fig.  8)  the  mercury  in  the  pipette  is  driven  to  g, 
and  m,  n,  and  y  are  then  closed.  Some  mercury  is  poured  into 
the  funnel  inserted  in  k,  and  i  is  opened.  Upon  lowering  the 
funnel  o  and  opening  the  pinchcock  n,  the  left  side  of  the  U- 
shaped  tube  B  can  easily  be  filled  down  to  a  mark  with  the  re- 
agent, for  the  mercury  drives  the  reagent  out  of  the  bulb  into  B. 
When  the  reagent  has  thus  been  measured  off,  i  is  closed,  y  is 
opened,  and  by  raising  the  funnel  o  the  reagent  is  driven  over 
into  the  pipette  until  the  mercury  reaches  the  point  x.  The 
pipette  is  then  disconnected,  the  capillary  d  is  immersed  in  a 
beaker  of  distilled  water,  and  by  careful  alternate  sucking  and 
blowing  at  /  the  capillary  is  freed  within  and  without  from  the 
last  traces  of  the  reagent.  It  is  then  dried  with  filter  paper,  and 
the  pipette  is  ready  for  use. 

2.  Solid  Phosphorus 

The  method  of  Lindemann  for  the  absorption  of  oxygen  by 
solid  phosphorus  gives,  under  proper  conditions  and  in  the  ab- 
sence of  gases  that  inhibit  the  reaction,  very  accurate  results. 
The  amount  of  phosphorus  contained  in  a  Hempel  gas  pipette 
is  capable  of  absorbing  a  very  large  volume  of  oxygen,  in  which 
respect  it  is  superior  to  alkaline  pyrogallol  which  has  a  rela- 
tively small  absorbing  power. 

Phosphorus  does  not,  however,  unite  with  oxygen  when  the 
gas  has  a  high  partial  pressure.  If  the  oxygen  is  nearly  pure, 
no  reaction  takes  place  between  it  and  phosphorus,  and  only 
when  its  pressure  is  lowered  either  by  dilution  with  another 
gas,  or  by  partial  exhaustion  with  an  air-pump,  does  a  union 
of  the  phosphorus  and  oxygen  result.  The  reaction  between 
the  two  elements  is  explosive  in  character  when  the  gas  mixture 
contains  from  50  to  75  per  cent  of  oxygen,  but  it  proceeds  quietly 
when  less  than  50  per  cent  of  oxygen  is  present.  It  is  unsafe 


164  GAS  ANALYSIS 

to  use  the  method  for  the  determination  of  oxygen  in  gas  mix- 
tures that  contain  enough  hydrogen  to  render  them  explosive, 
because  the  rise  of  temperature  caused  by  the  interaction  of 
the  phosphorus  and  oxygen  may  ignite  the  mixture.  In  such 
case,  or  when  the  mixture  contains  over  50  per  cent  of  oxygen, 
the  gas  should  be  absorbed  by  some  agent  other  than  phos- 
phorus. 

The  union  of  phosphorus  with  oxygen  is  prevented  or  greatly 
retarded  by  the  presence  of  even  small  amounts  of  certain  other 
gases,  such  as  ethylene,  acetylene,  some  other  hydrocarbons, 
some  ethereal  oils,  alcohol  or  ammonia. 

The  reaction  is  further  dependent  upon  the  temperature. 
It  proceeds  normally  at  about  20°  C.,  while  at  14°  it  takes  place 
quite  slowly,  so  that  a  quarter  of  an  hour  or  longer  is  required 
to  completely  separate  the  oxygen  from  100  cc.  of  air.  At  10° 
and  still  lower  temperatures  a  half  hour's  time  would  not  be 
sufficient.  It  follows  from  this  that  during  the  colder  months 
of  the  year  the  absorption  must  be  carried  out  in  warm 
rooms. 

The  absorption  of  oxygen  by  phosphorus  may  conveniently 
be  effected  by  passing  the  gas  mixture  into  a  Hempel  simple 
pipette  for  solid  and  liquid  reagents  (Fig.  35)  that  contains 
sticks  of  phosphorus  immersed  in  water. 

Phosphorus  may  be  purchased  on  the  market  in  the  form  of 
thin  sticks  ready  for  use,  or  it  may  be  prepared  by  the  analyst 
himself  in  this  form  in  the  following  manner:  —  A  test  tube  is 
filled  with  water,  and  sticks  of  phosphorus  of  the  ordinary 
commercial  size  are  introduced  into  the  tube.  The  tube  is  then 
placed  in  a  metal  water  bath  in  which  the  temperature  of  the 
water  is  maintained  at  about  50°.  The  phosphorus  readily 
melts  and  it  is  protected  from  the  action  of  the  air  by  the  water 
above  it.  Enough  phosphorus  should  be  used  to  form  in  the 
test  tube  a  column  of  molten  phosphorus  about  7  cm.  high. 
A  2-liter  beaker  full  of  cold  water  is  placed  near  the  water  bath. 
A  glass  tube  with  slight  taper  and  about  3  mm.  internal  diameter 


PROPERTIES  OF  THE  VARIOUS   GASES  165 

is  then  pushed  down  to  the  bottom  of  the  test  tube  containing 
the  molten  phosphorus,  the  upper  end  of  the  tube  is  closed  with 
the  moistened  finger,  and  the  tube,  carrying  a  column  of  the 
molten  phosphorus  with  a  little  water  above  it,  is  quickly  lifted 
out  of  the  test  tube  and  dipped  into  the  beaker  of  cold  water. 
If  the  walls  of  the  glass  tube  are  not  too  thick,  the  phosphorus 
soon  solidifies  and  since  it  decreases  in  volume  on  changing  from 
the  liquid  to  the  solid  state  the  stick  will  usually  fall  out  of  the 
tube  of  itself.  If  it  adheres  to  the  walls  it  may  easily  be  pushed 
out  with  a  wire.  The  cylindrical  part  of  the  gas  pipette  in  which 
the  phosphorus  is  to  be  placed  should  be  of  brown  glass  to  pro- 
tect the  phosphorus  from  the  action  of  the  light  (see  p.  56). 
If  such  pipettes  are  not  available  the  whole  pipette  when  not 
in  use  should  be  covered  by  a  light-tight  box  of  wood  or  card- 
board. The  pipette  is  filled  by  turning  it  upside  down,  removing 
the  stopper  of  the  cylindrical  portion,  filling  the  cylinder  with 
water,  and  then  introducing  the  small  sticks  of  phosphorus 
until  the  cylinder  is  tightly  packed  with  them.  The  stopper  of 
the  cylinder  is  then  inserted  and  the  pipette  is  turned  into  up- 
right position. 

In  the  absorption  of  oxygen  the  water  in  the  pipette  is  first 
driven  up  in  the  capillary  and  to  the  end  of  the  connecting  bent 
capillary  tube  by  blowing  into  a  rubber  tube  attached  to  the 
wide  tube  of  the  end  bulb.  The  connecting  capillary  tube  is 
then  inserted  into  the  rubber  tube  of  the  burette  and  the  gas 
mixture  is  passed  over  into  the  phosphorus  pipette,  the  water 
or  mercury  from  the  burette  being  allowed  to  follow  nearly  to 
the  cylinder  of  the  pipette.  The  union  of  the  phosphorus 
with  the  oxygen  is  complete  in  three "  minutes  or  less,  the 
end  of  the  reaction  being  shown  by  the  disappearance  of  the 
glow  when  the  pipette  is  in  a  dark  room.  Inasmuch  as  the  dif- 
ferent oxidation  products  of  phosphorus  are  soluble  in  water, 
the  surface  of  the  sticks  of  phosphorus  is  freed  from  these  sub- 
stances by  the  solvent  action  of  the  confining  water  provided 
the  water  is  renewed  from  time  to  time. 


1 66  GAS  ANALYSIS 


3.  Phosphorus  in  Solution 

Centnerszwer  has  suggested  1  the  employment  of  a  solution 
of  phosphorus  in  oil  as  an  absorbent  for  oxygen  in  gas  analytic 
work.  The  reagent  is  prepared  by  placing  about  230  cc.  of 
castor  oil  in  a  250  cc.  flask,  dropping  into  the  oil  three 
grams  of  well  dried  phosphorus,  and  after  lightly  closing  the 
neck  of  the  flask  with  a  stopper,  heating  the  contents  in  an  oil 
bath  to  200°.  The  hot  flask  is  then  removed  from  the  bath, 
the  stopper  is  tightly  inserted,  and  the  flask  is  wrapped  in  a 
towel  and  vigorously  shaken  until  complete  solution  of  phos- 
phorus is  effected.  When  cool  the  solution  is  ready  for  use. 
It  is  introduced  into  a  Hempel  double  absorption  pipette  for 
liquid  reagents  by  joining  to  the  wide  tube  of  the  pipette,  by 
means  of  a  piece  of  rubber  tubing,  a  wide  glass  tube  bent  down- 
ward, allowing  this  to  dip  into  the  oil  and  drawing  the  reagent 
into  the  further  bulbs  of  the  pipette  by  applying  suction  to 
the  capillary  tube  of  the  pipette. 

In  absorbing  oxygen,  the  gas  mixture  is  passed  over  into  the 
pipette  in  the  usual  manner  and  is  allowed  to  stand  in  contact 
with  the  oil  solution  of  phosphorus  as  long  as  a  glow  can  be  ob- 
served. No  harm  results  if  some  water  happens  to  pass  from 
the  burette  into  the  pipette.  After  the  glow  in  the  pipette  has 
disappeared,  the  remaining  gas  is  drawn  back  into  the  burette 
and  measured.  Centnerszwer  states  that  the  reagent  can  be 
used  for  the  determination  of  oxygen  in  gas  mixtures  that  are 
high  in  oxygen,  and  the  confirmatory  analyses  that  he  cites 
seem  to  show  that  the  method  is  fairly  accurate. 

4.  Copper 

A  very  active  absorbent  for  oxygen  is  metallic  copper  in  the 
form  of  little  rolls  of  wire-gauze,  immersed  in  a  solution  of  ammo- 
nia and  ammonium  carbonate. 

1  Chemiker-Zeitung,  34  (1910),  494. 


PROPERTIES  OF  THE  VARIOUS   GASES  167 

It  has  long  been  known  that  many  metals  oxidize  readily  in 
the  presence  of  vapor  of  ammonia.  The  absorption  of  oxygen, 
however,  takes  place  rapidly  only  so  long  as  the  metallic  sur- 
face is  bright,  and  it  proceeds  very  slowly  as  soon  as  consider- 
able quantities  of  oxide  are  formed. 

A  very  rapid  and  complete  absorption  of  oxygen  results  when 
the  gas  is  brought  into  contact  with  metallic  copper  and  a 
solution  consisting  of  equal  parts  of  a  saturated  solution  of  com- 
mercial ammonium  sesquicarbonate  and  a  solution  of  ammonia 
of  0.93  specific  gravity.  Such  an  ammoniacal  solution  has  a 
tension  that  may  in  most  cases  be  disregarded,  and,  provided 
the  absorption  apparatus  contains  sufficient  metallic  copper, 
the  solution  can  easily  absorb  24  times  its  volume  of  oxygen. 
Its  analytical  absorbing  power  is  therefore  6.  Since  the  sur- 
face of  metallic  copper  is  frequently  covered  with  a  thin  layer 
of  grease,  it  is  necessary  to  clean  it  before  using  by  exposing 
it  for  a  moment  to  the  action  of  nitric  acid. 

The  reagent  is  used  in  the  same  manner  as  solid  phos- 
phorus, in  a  pipette  for  solid  absorbents.  In  making  the 
absorption,  the  gas  is  allowed  to  remain  in  the  pipette  for  five 
minutes. 

The  method  described  admits  of  a  very  rapid  and  exact  de- 
termination of  oxygen.  As  compared  with  alkaline  pyrogallol, 
copper  has  a  much  greater  absorbing  power  for  oxygen,  and  it 
has  the  advantage  over  phosphorus,  aside  from  the  danger  at- 
tending the  use  of  the  latter,  of  absorbing  equally  well  at  any 
temperature,  while  the  absorption  of  oxygen  by  phosphorus 
takes  place  quite  slowly  at  temperatures  below  14°  C.  Di- 
rect experiments  showed  that  at  a  tejnperature  of  —  7°  C. 
the  absorption  of  oxygen  in  the  air  was  complete  in  five 
minutes. 

In  the  analysis  of  gas  mixtures  that  contain  carbon  monox- 
ide the  method  cannot  be  used,  because  the  basic  ammonium 
cuprous  carbonate,  formed  from  the  copper  present,  absorbs 
carbon  monoxide. 


i68  GAS  ANALYSIS 


5.  Solutions  of  Ferrous  Salts 

The  oxygen  in  gas  mixtures  containing  carbon  monoxide  can, 
according  to  Kostin,  be  removed  by  the  use  of  a  pipette  filled 
with  iron  wire  gauze  that  stands  in  a  saturated  solution  of  fer- 
rous sulphate  to  which  has  been  added  one-third  of  its  volume 
of  strong  ammonia.  It  is  preferable  to  employ  a  solution  of 
ferrous  chloride  to  which  has  been  added  ammonia  and  sufficient 
ammonium  chloride  to  prevent  the  separation  of  ferrous  hy- 
droxide. 

6.  Sodium  Hyposulphite 

Hyposulphurous  acid  was  first  prepared  in  1868  by  Schiitzen- 
berger.  The  formula  of  the  compound  was  correctly  determined 
by  Bernthsen  *  in  1880.  The  sodium  salt  of  the  acid  has  re- 
cently become  easily  obtainable  and  for  that  reason  Franzen  2 
has  examined  the  substance  with  a  view  to  ascertaining  whether 
it  could  be  used  in  gas  analysis  for  the  absorption  of  oxygen.  He 
prepares  the  reagent  by  dissolving  50  grams  of  sodium  hypo- 
sulphite in  250  cc.  of  water,  and  30  grams  of  sodium  hydroxide 
in  40  cc.  of  water,  and  mixing  the  two  solutions.  This  final 
solution  is  placed  in  a  Hempel  pipette  for  solid  reagents  that  has 
first  been  filled  with  small  rolls  of  iron  wire  gauze.  Franzen 
states  that  in  this  apparatus  oxygen,  if  present  in  not  too  large 
amount,  is  completely  absorbed  in  five  minutes.  The  reaction 
that  takes  place  is  represented  by  the  equation 

2Na2S2O4  +  2  H2O  +  O2  =  4  NaHS03, 

from  which  it  appears  that  one  gram  of  sodium  hyposulphite  is 
able  to  absorb  about  64  cc.  of  oxygen.  One  cc.  of  the  above 
solution  will  consequently  absorb  10.7  cc.  of  oxygen,  and  its 
analytical  absorbing  power  (see  p.  65)  will  therefore  be  about 
2.5.  Franzen  enumerates  the  following  advantages  possessed 

1  Berichte  der  deutschen  chemischen  Gesellschaft,  13  (1880),  2277. 

2  Berichte  der  deutschen  chemischen  Gesellschaft,  39  (1906),  2069. 


PROPERTIES  OF  THE   VARIOUS   GASES  169 

by  sodium  hyposulphite  over  other  absorbents  for  oxygen.  In 
the  first  place  it  is  decidedly  cheaper  than  pyrogallol; 1  secondly, 
it  absorbs  oxygen  as  rapidly  at  low  temperatures  as  it  does  at 
higher,  whereas  the  absorbing  power  of  alkaline  pyrogallol  and 
of  phosphorus  shows  marked  decrease  with  fall  of  temperature. 
Furthermore  the  absorption  of  oxygen  by  the  reagent  is  not 
influenced  by  gases  that  prevent  the  oxidation  of  phosphorus. 

If  the  reagent  is  to  be  used  in  the  Bunte  burette  for  the  deter- 
mination of  oxygen  Franzen  recommends  the  use  of  a  solution 
somewhat  less  concentrated  than  that  described  above,  and 
employs  for  this  purpose  a  solution  of  ten  grams  of  sodium 
hyposulphite  in  50  cc.  of  water  to  which  has  been  added  50  cc. 
of  a  ten  per  cent  solution  of  sodium  hydroxide.  Shaking  for 
three  minutes  suffices  to  completely  remove  the  oxygen  when 
that  gas  is  present  in  not  too  great  amount. 

7.  Chromous  Chloride 

Chromous  chloride  may  be  used  for  absorbing  oxygen  2  in  the 
presence  of  hydrogen  sulphide  and  carbon  dioxide.  These  two 
gases  are  completely  indifferent  to  both  the  blue  chromic  chloride 
and  the  green  chromous  chloride  solutions. 

Dennstedt  and  Hassler,  however,  state  3  that  as  an  absorbent 
for  oxygen  it  is  open  to  objection  because  it  easily  gives  off 
hydrogen. 

To  prepare  chromous  chloride,  Von  der  Pfordten  has  used  the 
method  given  by  Moissan.  A  green  solution  of  chromic  chloride 
free  from  chlorine  is  made  by  heating  chromic  acid  with  concen- 
trated hydrochloric  acid,  and  this  solution  is  then  reduced  with 
zinc  and  hydrochloric  acid.  Since  spongy  particles  always 
separate  from  the  zinc  used  for  the  reduction,  the  solution  must 
be  filtered.  For  this  purpose  the  reduction  is  carried  on  in  a 
flask  fitted  with  a  long  and  a  short  tube,  as  is  a  wash-bottle. 

1  The  German  price  lists  for  191 1  quote  about  $1.00  per  kilogram. 

2  Otto  von  der  Pfordten,  Liebig's  Annalen,  228  (1885),  112. 

3  Berichte  der  deutschen  chemischen  Gesettschaft,  41  (1908),  2780. 


i  yo  GAS  ANALYSIS 

The  longer  tube  is  bent  downward  above  the  flask  and  is  here 
supplied  with  a  small  bulb-tube,  which  is  filled  with  glass-wool 
or  asbestos.  The  hydrogen  given  off  during  the  reduction  is 
allowed  to  pass  out  through  the  longer  tube  for  some  time;  then 
after  closing  its  outer  end  the  tube  is  pushed  down  into  the  solu- 
tion. The  hydrogen  is  thus  obliged  to  pass  out  through  the 
shorter  tube,  which  carries  a  rubber  valve.  Carbon  dioxide  is 
then  passed  into  the  flask  through  the  short  tube,  and  the 
chromous  chloride  solution  is  driven  over  into  a  beaker  contain- 
ing a  saturated  solution  of  sodium  acetate;  a  red  precipitate  of 
chromous  acetate  is  formed  which  is  washed  by  decantation 
with  water  containing  carbonic  acid.  The  red  chromous  acetate 
is,  relatively  speaking,  quite  stable,  and  in  moist  condition  it 
may  be  kept  for  an  unlimited  time  in  closed  bottles  filled  with 
carbon  dioxide. 

In  washing  the  red  precipitate,  some  free  acetic  acid  is  added 
in  the  beginning,  to  dissolve  any  basic  zinc  carbonate  which 
may  have  been  thrown  down.  In  this  way  a  preparation  com- 
pletely free  from  zinc  is  obtained. 

To  absorb  oxygen,  the  chromous  acetate  is  decomposed  by 
the  addition  of  hydrochloric  acid,  the  air  being  excluded.  It  is 
advisable  to  use  an  excess  of  chromous  acetate  in  order  to  avoid 
the  presence  of  free  hydrochloric  acid. 

OZONE 

Properties  of  Ozone.  —  Specific  Gravity  =  1.62. 

Ozone,  Os,  is,  at  ordinary  temperatures,  a  gas  that  possesses 
a  peculiar,  pungent  odor.  In  a  layer  one  meter  thick  it  shows  a 
distinctly  blue  color.  It  has  a  marked  irritating  effect  on  the 
mucous  membrane.  It  is  a  powerful  oxidizing  agent. 

The  Detection  of  Ozone.  —  The  detection  of  ozone,  particu- 
larly in  such  small  amounts  as  may  be  present  in  atmospheric 
air,  has  frequently  been  the  subject  of  investigation,  and  many 
agents  and  many  methods  for  accomplishing  the  object  have 
been  described  in  the  chemical  journals. 


PROPERTIES  OF  THE  VARIOUS   GASES 


171 


It  has  been  found  particularly  difficult  to  identify,  in  the 
presence  of  one  another,  the  three  gases  ozone,  nitrogen  tetroxide 
(peroxide)  and  hydrogen  dioxide.  This  problem  appears  to  have 
been  satisfactorily  solved  by  Keiser  and  McMaster,1  who  have 
also  given  an  admirable  summary  of  the  earlier  work  that  has 
been  done  in  this  field.  For  these  reasons  their  article  is  here 
quoted  in  full: 

"When  air  is  acted  upon  in  a  number  of  ways,  such  as  by 
electric  sparks,  the  flaming  arc,  burning  hydrogen,  burning 
magnesium,  heated  platinum  wire,  etc.,  in  short,  by  any  means 
which  produce  very  high  temperatures,  ozone,  nitrogen  peroxide, 
and  hydrogen  peroxide  may  be  formed.  The  silent  electric  dis- 
charge and  the  slow  oxidation  of  phosphorus  produce  oxidizing 
gases  in  air.  Several  commercial  processes  of  treating  air  so  as 
to  convert  it  into  a  more  active  chemical  agent  are  at  present  in 
use.  It  is  desirable,  therefore,  to  have  characteristic  reactions 
for  each  of  the  three  substances  above  mentioned  in  examining 
the  gases  produced  in  these  different  ways. 

"  A  great  many  reagents  have  been  suggested  for  this  purpose, 
but  many  of  these  have  been  found  to  be  unreliable,  while  others 
are  not  very  sensitive,  and  still  others  are  rare  substances  that 
are  not  easily  obtained.  The  following  table  contains  a  list  of 
such  substances,  together  with  a  statement  of  their  behavior 
toward  ozone,  nitrogen  peroxide,  and  hydrogen  peroxide. 


Ozone 

Nitrogen 
peroxide 

Hydrogen 
peroxide 

Potassium  iodide  and  starch  2    . 

blue 

blue 

blue 

Wine-red    litmus    paper    mois- 

tened with  potassium  iodide  3 

blue 

no  change 

blue 

Tetramethylparaphenylenedia- 

mine  4        

bluish  violet 

bluish  violet 

bluish  violet 

1  Amer.  Chem.  J.,  39  (1908),  96. 

2  Schoenbein:  Ber.  u.  d.  Verh.  d.  Nat.  Ges.,  Basel,  4,  58. 

3  Houzeau:  Compt.  rend.  45,  873'. 

4  Wurster:  Ber.  d.  deutsch.  chem.  Ges.,  19,  3195. 


172 


GAS  ANALYSIS 


Ozone 

Nitrogen 
peroxide 

Hydrogen 
peroxide 

Metaphenylenediamine,  alkaline 

Burgundy 

solution  l      

red  or  yellow 

no  change 

no  change 

Manganese  chloride  paper  mois- 

tened with  guiacum  tincture  2 

blue 

blue 

no  change 

Benzidine  in  alcohol  3       .      . 

brown 

blue 

no  change 

Tetramethyl-^-^-diaminodiphen- 

ylmethane    in    saturated 

alcoholic  solution  4        ... 

violet 

yellow 

no  change 

Potassium  ferricyanide  and  ferric 

chloride  5      

no  change 

no  change 

blue 

Manganese    dioxide    or    copper 

oxide  6     

decomposed 

no  change 

decomposed 

Silver  foil  7 

black 

no  change 

no  change 

Chromic  acid  and  ether  8 

no  change 

no  change 

blue 

Chromic  acid  9       

no  change 

decomposed 

Titanium  hydroxide  in  sulphuric 

acid  10     

no  change 

no  change 

yellow 

Thallous  salts  "    

brown 

no  change 

no  change 

Ammonium    molybdate   in    sul- 

phuric acid  12     .      .      .      •.     . 

no  change 

no  change 

yellow 

Guiacum  tincture  with  malt  in- 

fusion 13 

no  change 

no  change 

blue 

Gold  chloride  free  from  acid  14    . 

black 

no  change 

Nitrite  test  with  sulphanilic  acid 

and  o-naphthylamine  15 

no  change 

pink 

no  change 

1  Erlwein  and  Weyl:  Ibid.,  31,  3158. 

2  Engler  and  Wild:  Ibid,,  29,  1940. 

3  Arnold  and  Mentzel:  Ibid.,  35,  1324. 

4  Ibid. 

6  Schoenbein,  Weltzien,  also  Schoene:  Ibid.,  7,  1695.  Engler  and  Wild:  Ibid.,  29, 
1940. 

6  Andrews  and  Tait:  Ann.  Chem.  (Liebig),  112,  185. 

7  Ber.  d.  deutsch.  chem.  Ges.,  35,  1326. 

8  Barreswill:  Ann.  chim.  phys.  (3),  20,  364. 

9  Engler  and  Wild:  Ber.  d.  deutsch.  chem.  Ges.,  29,  1940. 

10  Schoenn:  Z.  anal.  Chem.,  9,  41. 

11  Schoene:  Ann.  Chem.  (Liebig),  196,  58. 

12  Schoenn:  Z.  anal.  Chem.,  9, 41. 

13  Struve:  Ibid.,  8,  315. 

14  Boettger:  Ibid.,  19,  105. 

15  Bull.  Soc.  Chim.  (3),  2,  347  (1889). 


PROPERTIES   OF  THE  VARIOUS   GASES  173 

"  Arnold  and  Mentzel 1  have  studied  a  number  of  the  reagents 
that  are  mentioned  in  the  preceding  list.  They  find  that  potas- 
sium iodide  and  starch,  and  zinc  iodide  and  starch,  as  well  as 
guiacum  tincture,  give  a  blue  color  with  ozone,  nitrogen  per- 
oxide, chlorine,  and  bromine.  In  short,  these  reagents  are  not 
characteristic  of  anything  more  than  an  oxidizing  gas.  Red 
litmus  paper  moistened  with  potassium  iodide  solution  they  find 
to  be  entirely  unreliable,  because  all  paper  turns  blue  with  free 
iodine,  and  any  gas  that  liberates  iodine  will  turn  the  paper  blue. 
They  also  found  that  a  solution  of  potassium  iodide  to  which 
wine-red  litmus  solution  had  been  added  was  unsatisfactory, 
because  the  ozone  acts  upon  the  litmus  and  changes  it  to  a  green 
color.  The  third  reagent  in  the  above  list,  tetramethylpara- 
phenylenediamine,  is  also  turned  blue  by  all  oxidizing  gases. 
Metaphenylenediamine,  the  fourth  one,  was  unsatisfactory  be- 
cause they  found  that  nitrogen  peroxide  gave  the  same  color  as 
ozone,  and  all  oxidizing  gases  give  yellowish  colors  with  this  sub- 
stance. Silver  foil  2  is  not  satisfactory  because  it  is  not  at  all 
sensitive.  Arnold  and  Mentzel  recommend  an  alcoholic  solution 
of  benzidine  or,  still  better,  an  alcoholic  solution  of  tetramethyl- 
/>-/>-diaminodiphenylmethane.  This  gives  a  violet  color  with 
ozone  and  yellow  with  nitrogen  peroxide;  with  hydrogen  perox- 
ide it  remains  unchanged.  They  found,  however,  that  the  ozone 
obtained  by  the  action  of  sulphuric  acid  upon  barium  dioxide 
had  a  different  action  upon  this  reagent;  instead  of  violet  a  green 
color  was  obtained.  Benzidine,  under  the  same  conditions, 
gave  a  blue  instead  of  a  brown  color.  Similar  effects  were  ob- 
tained with  the  ozone  from  persulphates,  percarbonates,  and 
from  sodium  and  hydrogen  peroxides.  • 

"F.  Fischer  and  Marx  3  have  used  tetramethyl-/>-/>-diarninodi- 

1  Ber.  d.  deutsch.  chem.  Ges.,  35,  (1902)  1324. 

2  Manchot  and  Kampschulte  (Ber.  d.  deutsch.  chem.  Ges.,  40,  [1907]  2891)  have 
recently  shown  that  while  silver  foil  is  not  at  all  sensitive  at  ordinary  temperatures, 
it  becomes  much  more  so  at  22o°-24o°  C.    For  metallic  mercury  they  found  the 
temperature  at  which  action  was  strongest  to  be  170°  C. 

3  Ber.  d.  deutsch.  chem.  Ges.,  39,  (1906)  2555. 


174  GAS  ANALYSIS 

phenylmethane  or  '  tetramethyl  base,'  as  it  is  called,  in  their 
investigations  upon  the  formation  of  ozone  and  nitrogen  peroxide 
in  air  at  high  temperatures.  They  prepared  ozone  by  the  silent 
electric  discharge  in  the  Siemen's  ozonometer,  by  the  action  of 
ultraviolet  light,  by  the  electrolysis  of  sulphuric  acid,  and  in 
other  ways,  and  found  that  ozone  produces  with  this  reagent  a 
violet  color  and  the  oxides  of  nitrogen  a  yellow  color.  Mixtures 
of  both  gases  give  a  dirty  brown  color  intermediate  between 
violet  and  yellow.  Another  fact  that  they  emphasize  is  that  the 
paper  must  always  be  kept  moist;  if  it  becomes  dry,  ozone 
changes  it  to  a  yellow  color.  To  detect  very  small  quantities  of 
nitrogen  oxides  in  the  presence  of  ozone  they  recommend  that 
the  gas  be  conducted  into  liquid  air.  The  ozone  will  dissolve 
while  the  oxides  of  nitrogen  will  separate  as  blue  flakes.  When 
the  liquid  air  is  then  filtered,  the  frozen  oxides  of  nitrogen  re- 
main upon  the  filter.  The  filtrate  is  allowed  to  boil,  the  air 
distils  away,  and  the  ozone  remains.  In  this  way  both  can  be 
separately  identified. 

"This  method  is  open  to  the  objection  that  liquid  air  is  not 
readily  obtained  in  many  places.  Likewise  the  '  tetra  base '  of 
Wurster  and  the  'tetramethyl  base'  of  Arnold  and  Men tzel  are 
not  easily  obtainable  substances.  Moreover,  the  color  changes 
are  not  always  satisfactory.  Thallous  salts  and  titanic  acid  are 
not  always  on  hand.  We  have  now,  however,  devised  a  method 
which  is  free  from  these  objectionable  features  and  enables  us  to 
identify  each  of  these  three  substances  in  the  presence  of  others. 

"We  found  that  potassium  permanganate,  even  in  very  di- 
lute solution,  is  not  decolorized  by  ozone.  Nitrogen  peroxide 
and  hydrogen  peroxide,  on  the  other  hand,  both  reduce  it  in- 
stantly. To  identify  ozone  in  gases  that  contain  at  the  same 
time  nitrogen  peroxide  and  hydrogen  peroxide  it  is  only  necessary 
to  draw  the  gases  through  a  solution  of  potassium  permanganate; 
the  nitrogen  peroxide  and  hydrogen  peroxide  will  not  pass 
through,  while  the  ozone  will,  and  can  then  be  detected  with 
potassium  iodide  and  starch. 


PROPERTIES   OF  THE   VARIOUS   GASES  175 

"To  detect  nitrogen  peroxide  in  the  presence  of  ozone  and 
hydrogen  peroxide  we  take  advantage  of  the  fact  that  both 
ozone  and  hydrogen  peroxide  are  decomposed  when  passed 
through  a  tube  containing  powdered  manganese  dioxide.  Nitro- 
gen peroxide  passes  through  unchanged.  Its  presence  can  be 
shown  by  passing  the  gas,  after  it  has  gone  over  the  manganese 
dioxide,  into  very  dilute  permanganate.  If  the  latter  is  decolor- 
ized, nitrogen  peroxide  was  present.  A  still  more  delicate  test 
for  nitrogen  peroxide  is  this:  pass  the  gas,  which  may  contain 
ozone  and  hydrogen  dioxide,  directly  into  pure  caustic  soda, 
made  from  metallic  sodium  and  nitrite-free  distilled  water,  and 
then  test  the  caustic  soda  solution  for  nitrites  by  the  well-known 
sulphanilic  acid  and  a-naphthylamine  method. 

"Hydrogen  dioxide  can  be  identified  in  the  presence  of  both 
ozone  and  nitrogen  peroxide  by  passing  the  gas  mixture  into  a 
solution  of  potassium  ferricyanide  and  ferric  chloride.  The 
yellow  brown  solution  becomes  green  and  then  blue  as  more 
hydrogen  dioxide  passes  in.  This  formation  of  Prussian  blue  is 
characteristic  of  hydrogen  dioxide  and  is  not  produced  by 
either  ozone  or  nitrogen  peroxide.  This  we  have  found  by 
experiment. 

"  Examination  of  the  Gases  Produced  by  Burning  Hy- 
drogen in  Air.  —  We  have  triecl  our  method  in  the  examination 
of  the  gases  produced  by  burning  hydrogen  in  air.  A  jet  of 
burning  hydrogen  was  introduced  into  the  end  of  a  glass  tube 
fifteen  millimeters  in  diameter.  A  current  of  air  was  drawn  into 
the  tube  by  means  of  an  aspirator.  The  gas  passed  from  the 
tube  through  a  moderately  strong  solution  of  potassium  perman- 
ganate and  then  into  a  solution  of  potassium  iodide  and  starch. 
This  soon  became  blue,  thus  showing  that  ozone  was  formed 
by  the  hydrogen  burning  in  a  rapid  current  of  air.  The  potas- 
sium permanganate  wash  bottle  was  then  replaced  by  a  tube 
forty  centimeters  in  length,  filled  with  powdered  manganese 
dioxide.  Between  this  tube  and  the  aspirator,  a  wash  bottle 
with  a  very  weak  solution  of  potassium  permanganate  was  in- 


1 76  GAS  ANALYSIS 

serted.  Air  was  now  rapidly  drawn  through  the  apparatus  and 
the  products  of  combustion  of  the  hydrogen  passed  first  over 
the  manganese  dioxide  and  then  into  the  dilute  permanganate. 
The  latter,  after  a  time,  became  decolorized,  thus  showing  that 
nitrogen  peroxide  was  formed.  This  was  confirmed  by  passing 
the  gases  formed  by  burning  hydrogen  into  a  solution  of  nitrite- 
free  caustic  soda  and  then  applying  the  nitrite  test  (Griess  test) 
after  having  slightly  acidified  the  solution.  The  pink  color  was 
formed,  thus  confirming  the  result  obtained  with  dilute  per- 
manganate. The  gases  formed  by  burning  hydrogen  were  also 
tested  for  hydrogen  peroxide  by  drawing  them  through  a  solu- 
tion of  potassium  ferricyanide  and  ferric  chloride.  This  became 
first  green,  then  blue,  thus  showing  that  hydrogen  peroxide  was 
present.  This  ferricyanide  and  ferric  chloride  test  for  hydrogen 
peroxide  we  found  to  be  more  sensitive  than  titanium  dioxide  in 
sulphuric  acid.  The  latter  failed  to  show  the  presence  of  hydro- 
gen peroxide  in  the  gases  produced  by  burning  hydrogen  in  air. 

"  Examination  of  the  Gases  Produced  by  the  Silent  Elec- 
tric Discharge  in  Air  and  Oxygen.  —  Atmospheric  air  was 
purified  and  dried  by  being  drawn,  by  means  of  an  aspirator, 
through  a  series  of  wash  bottles  containing  silver  sulphate,  potas- 
sium permanganate,  and  pure  concentrated  sulphuric  acid,  and 
was  then  passed  through  a  Siemen's  ozonometer.  The  ozonometef 
was  connected  with  the  terminals  of  a  Ruhmkorff  coil  which,  in 
turn,  was  connected  with  a  storage  battery.  The  potential  of  the 
coil  discharge  terminals  was  2160  volts.  The  air  passing  through 
the  ozonometer  in  which  the  silent  discharge  was  taking  place 
was  thereupon  conducted  through  a  very  weak  solution  of  potas- 
sium permanganate.  No  decolorization  took  place,  although 
the  ozonized  air  was  passed  for  more  than  two  hours.  Ozone 
was  shown  to  be  present  in  quantity,  not  only  by  its  action  upon 
potassium  iodide  and  starch  after  it  had  passed  through  the 
permanganate,  but  also  by  its  odor  and  by  the  repeated  perfora- 
tion of  the  rubber  tube  that  connected  the  last  wash  bottle  with 
the  aspirator.  We  were  surprised  to  find  that,  under  these  con- 


PROPERTIES   OF  THE   VARIOUS   GASES  177 

ditions,  no  nitrogen  peroxide  was  formed.  A  quantitative  de- 
termination of  the  ozone  showed  that  there  was  0.00086  gram 
per  liter.  We  also  conducted  the  air  directly  from  the  ozonom- 
eter  into  pure  caustic  soda  and  tested  this  for  nitrites  by  the 
Griess  test  but  failed  to  obtain  any.  With  potassium  ferri- 
cyanide  and  ferric  chloride  the  ozonized  air  failed  to  give  a  re- 
action for  hydrogen  peroxide.  The  same  results,  namely,  the 
absence  of  nitrogen  peroxide  and  hydrogen  peroxide  in  air  that 
had  passed  through  the  Siemen's  ozonometer,  were  obtained 
when  we  omitted  washing  the  air  with  silver  sulphate,  caustic 
soda,  potassium  permanganate,  and  sulphuric  acid  before  it 
entered  the  ozonometer.  These  experiments  show  conclusively 
that  it  is  possible  to  ozonize  air  without,  at  the  same  time,  form- 
ing nitrogen  peroxide  and  hydrogen  peroxide.  We  have  repeated 
the  above  experiments  with  oxygen,  made  from  fused  sodium 
peroxide  and  water,  instead  of  air.  We  obtained  no  nitrogen 
peroxide  nor  hydrogen  peroxide.  A  quantitative  determina- 
tion showed  the  presence  of  0.0012  gram  of  ozone  to  the  liter. 
This  ozonized  oxygen  failed  to  decolorize  potassium  perman- 
ganate solution. 

"  Examination  of  Gases  Produced  by  the  Action  of  Con- 
centrated Sulphuric  Acid  upon  Barium  Dioxide.  —  Concen- 
trated sulphuric  acid  was  allowed  to  drop  upon  barium  dioxide, 
contained  in  an  Erlenmeyer  flask,  and  the  gases  resulting  were 
conducted  through  a  concentrated  solution  of  potassium  per- 
manganate in  a  Geissler  potash  bulb,  and  then  into  a  solution 
of  potassium  iodide  and  starch.  A  blue  color  soon  appeared, 
thus  showing  the  presence  of  ozone.  The  gas,  after  passing 
over  manganese  dioxide  and  then  into*  permanganate,  failed 
to  give  the  reaction  for  nitrogen  peroxide.  Nor  were  we  able 
to  detect  hydrogen  peroxide  by  passing  the  gas  through  a  solu- 
tion of  potassium  f erricyanide  and  ferric  chloride. 

"A  small  quantity  of  barium  nitrate  was  now  added  to  the 
barium  dioxide,  and,  on  treating  with  concentrated  sulphuric 
acid  and  testing  as  before,  we  obtained  evidence  of  the  presence 


iy8  GAS  ANALYSIS 

of  ozone  and  nitrogen  peroxide,  but  not  of  hydrogen  peroxide, 
in  the  gases  given  off. 

"  Examination  of  the  Gases  Produced  by  the  Slow  Oxida- 
tion of  Phosphorus  in  Moist  Air.  —  We  have  also  used  our 
method  for  the  examination  of  the  gases  formed  by  the  slow 
oxidation  of  phosphorus  in  air  in  the  presence  of  water.  We 
found  ozone  and  nitrogen  peroxide  but  no  hydrogen  per- 
oxide. 

"  Examination  of  the  Gases  Produced  by  the  Action  of 
the  Flaming  Electric  Arc  upon  Air.  —  Air  that  had  passed 
through  the  flaming  electric  arc  of  an  Alsop  process  machine, 
such  as  is  used  in  treating  flour,  was  next  examined  by  our 
method.  We  found  that  this  air  contained  nitrogen  peroxide,  a 
trace  of  ozone,  and  a  little  hydrogen  peroxide. 

"Examination  of  Atmospheric  Air.  —  We  have  applied  our 
method  to  the  examination  of  country  air.  Air  from  outside  of 
the  laboratory  was  drawn  through  a  layer  of  absorbent  cotton, 
six  inches  in  length,  then  through  a  concentrated  solution  of 
potassium  permanganate  in  a  potash  bulb,  and  finally  into 
potassium  iodide  and  starch.  After  the  air  had  passed  through 
for  five  hours,  a  faint  blue  color  appeared,  thus  showing  the 
presence  of  ozone.  Air  that  was  filtered  through  absorbent 
cotton  and  that  had  passed  over  a  layer  of  manganese  dioxide 
eighteen  inches  in  length  was  conducted  through  a  very  faintly 
pink  solution  of  permanganate.  No  decolorization  was  ob- 
served, although  the  air  was  drawn  through  for  eighteen  hours. 
We  conclude  from  this  that  there  was  no  nitrogen  peroxide  in 
the  air.  Air  filtered  through  cotton  was  drawn  through  a  solu- 
tion of  potassium  ferricyanide  and  ferric  chloride.  After  four 
hours  the  solution  acquired  a  green  color.  We  found,  however, 
that  the  reagent  used  for  detecting  hydrogen  dioxide,  namely,  a 
dilute  solution  of  ferric  chloride  and  potassium  ferricyanide, 
when  allowed  to  stand  in  air,  gradually  forms  a  green  precipitate, 
even  when  protected  from  dust  by  being  covered  with  a  bell  jar. 
We,  therefore,  drew  atmospheric  air  for  five  hours  through  pure 


PROPERTIES   OF  THE  VARIOUS   GASES  179 

distilled  water,  contained  in  a  potash  bulb,  and  then  tested  this 
water  with  the  reagent.  We  obtained  no  blue  precipitate,  and, 
therefore,  conclude  that  the  green  color  mentioned  above  may 
not  have  been  caused  by  hydrogen  dioxide.  These  experiments 
prove  that  our  method  is  sufficiently  sensitive  to  show  the  pres- 
ence of  ozone  in  atmospheric  air." 

Determination  of  Ozone.  —  An  excellent  method  for  the 
determination  of  ozone  is  that  perfected  by  Treadwell  and 
Anneler,1  in  which  the  ozonized  oxygen  is  caused  to  act  upon  a 
neutral  solution  of  potassium  iodide, 

2  KI  +  03  +  H2O  =  2  KOH  +  2  I  +  O2. 

The  liberated  iodine  is  titrated  with  j^  sodium  thiosulphate 
after  first  acidifying  the  solution  with  dilute  sulphuric  acid, 
i  cc.  —  Na2S2O3  =  0.0024  gram  OB. 

An  acid  solution  of  potassium  iodide  may  not  be  employed 
because  hydrogen  dioxide  is  then  formed  and  this  sets  free  a 
further  amount  of  iodine. 

4  O3  +  10  HI  +  H2O  =  10 1  +  3  O2  +  H2O2  +  5  H2O. 

The  gas  sample  is  collected  and  measured  in  a  bulb  of  the  form 
shown  in  Fig.  78,  which  is  a  slight  modification  of  that  proposed 
by  Treadwell.  The  bulb,  B,  has  a  capacity  of  from  300  cc.  to 
400  cc.  and  its  volume  is  accurately  determined  by  weighing 
it  empty  and  then  filled  with  water,  applying  correction  for  tem- 
perature.2 The  carefully  ground  slip-joint  of  glass,  A,  serves  to 
connect  the  bulb  with  the  apparatus  from  which  the  ozonized  air 
is  to  be  drawn.  Rubber  or  cork  connections  may  not  be  used 
because  both  are  attacked  by  ozone. 

The  bulb  is  filled  with  distilled  water,  and  the  gas  sample  is 
drawn  in  through  A  by  opening  both  stopcocks  and  allowing  the 

1  Z.f.  anorg.  Chem.,  48  (1905),  86. 

2  See  Analytical  Chemistry  by  Treadwell,  translated  by  Hall  (1911),  vol.  II,  p.  678. 


i8o 


GAS  ANALYSIS 


water  to  flow  out.  The  lower  stopcock  H  is  then  closed,  and  a 
few  seconds  later  the  upper  stopcock  C  is  closed.  The  inlet  tube 
D  is  now  removed  and  the  stopcock  C  is  opened  for  an  instant 
to  bring  the  gas  to  atmospheric  pressure.  The  barometric 
pressure  and  the  temperature  of  the  room  are  read  and 
recorded. 

The  tube  below  H  is  connected  by  a  piece  of  rubber  tubing 
with  the  level-bulb  S  which  is  then  filled  with  a  twice-normal  so- 
lution of  potassium  iodide.  Air 
in  the  rubber  tube  is  driven  out 
through  the  end  opening  of  the 
tail-stopper  H,  and  the  stopper 
is  then  turned  and  from  20  cc. 
to  30  cc.  of  the  solution  is  forced 
into  the  bulb.  H  is  now  closed 
and  the  rubber  tube  is  taken  off. 
The  bulb  is  vigorously  shaken 
and  allowed  to  stand  for  about 
half  an  hour,  at  the  end  of 
which  time  the  absorption  of 
ozone  will  be  complete.  The  so- 
lution in  the  bulb  is  then  run 
out  into  an  Erlenmeyer  flask, 
the  bulb  being  rinsed  with  a 
small  volume  of  the  solution  of 
potassium  iodide  and  then  finally 
with  distilled  water.  The  solu- 
tion is  acidified  with  dilute  sul- 
phuric acid  and  the  free  iodine 

is  titrated  with  a  ~  solution  of  sodium  thiosulphate.  In  com- 
puting the  per  cent  of  ozone  in  the  gas  mixture,  the  vol- 
ume v  of  the  gas  sample  in  the  bulb  is  first  corrected  to 
the  volume  VQ  that  it  would  occupy  under  standard  con- 
ditions by  means  of  the  formula  given  on  page  35.  If  n 


FIG. 


PROPERTIES  OF  THE  VARIOUS   GASES  181 

represents  the  number  of  cubic  centimeters  of  j^  sodium  thio- 
sulphate  used  in  the  titration  of  the  free  iodine,  then 

112  x  n 
per  cent  by  volume  of  ozone  =  

Vo 

Treadwell  and  Anneler  do  not  discuss  the  possibility  of  inter- 
ference by  nitrogen  peroxide  or  hydrogen  peroxide  in  their 
method  for  the  determination  of  ozone  nor  do  they  describe  any 
procedure  for  the  removal  of  these  gases.  The  ozone  could 
probably  be  freed  from  the  two  gases  by  passing  the  mixture 
through  a  solution  of  potassium  permanganate  as  recommended 
by  Keiser  and  McMaster  (page  174). 

HYDROGEN 

Properties  of  Hydrogen.  —  Specific  gravity,  0.06965 ;  weight 
of  one  liter,  0.09004;  boiling  point,  —  252°. 
According  to  L.  W.  Winkler,1  one  volume  of  water  absorbs  at 

o°,  0.02148  vol.  hydrogen 

5°,  0.02044 
10°,  0.01955 
15°,  0.01883 
20°,  0.01819 

At  f  alcohol  takes  up 

0.06925  —  0.0001487*  +  o.oooooi*2  vol.  of  hydrogen; 
hence  at 

20°,  0.066676  vol.  (Bunsen). 

Detection  of  Hydrogen.  —  For  the  detection  of  hydrogen 
Phillips  2  recommends  the  use  of  dry  palladious  chloride  which 
reacts  with  hydrogen  with  the  formation  of  hydrogen  chloride 
that  then  causes  precipitation  of  silver  chloride  when  the  issuing 

1  Berichte  der  deutschen  chemischen  Gesellschaft,  24  (1891),  89.    See  also  Timofejew, 
Zeitschr.fiir  phys.  Chem.,  6  (1890),  141. 

2  American  Chemical  Journal,  16  (1894),  259. 


182  GAS  ANALYSIS 

gases  are  passed  through  a  solution  of  silver  nitrate.  Since, 
however,  palladious  chloride  is  reduced  by  the  olefines  and  by 
carbon  monoxide  the  method  is  applicable  to  the  detection  of 
hydrogen  only  in  such  gas  mixtures  as  do  not  contain  these  con- 
stituents. Zenghelis  1  has  recently  described  a  method  that  may 
be  used  for  the  detection  of  hydrogen  in  the  presence  of  such 
hydrocarbons  as  methane,  ethylene  and  acetylene.  It  consists 
in  passing  the  gas  mixture  through  a  solution  of  sodium  hydrox- 
ide and  then  through  a  tube  fitted  with  a  tip  of  platinum  foil  or 
platinum  wire  gauze.  The  foil  or  gauze  should  be  carefully 
ignited  before  the  test  is  made.  This  delivery  tube  is  immersed 
in  a  few  cubic  centimeters  of  a  warm  solution  of  sodium  molyb- 
date  contained  in  a  test  tube.  The  reagent  is  prepared  by  dis- 
solving one  gram  of  molybdenum  trioxide  in  dilute  sodium 
hydroxide,  adding  dilute  hydrochloric  acid  in  slight  excess  and 
diluting  to  200  cc.  with  water.  When  molecular  hydrogen 
passes  through  the  delivery  tube  it  is  occluded  by  the  platinum 
and  in  this  condition  immediately  reduces  the  ammonium  molyb- 
date  solution,  imparting  to  the  latter  an  intense  blue  color.  If 
the  amount  of  hydrogen  is  very  small  or  if  the  molybdenum 
solution  is  cold,  the  color  is  a  light  greenish  blue.  Palladium  is 
to  be  preferred  to  platinum  in  testing  for  hydrogen  by  this 
method,  but  the  latter  metal  gives  quite  satisfactory  results 
unless  there  is  only  a  trace  of  hydrogen  in  the  gas  mixture. 
Arsine,  phosphine  and  carbon  monoxide  will  cause  the  reduction 
of  the  molybdenum  solution  and  consequently  these  three  gases 
must  be  removed  before  the  test  for  hydrogen  is  made. 

Determination  of  Hydrogen  by  Absorption. —  A  method  for 
the  volumetric  determination  of  hydrogen  by  means  of  a  liquid 
absorbent  has  recently  been  described  by  Paal  and  Hartmann.2 
They  employ  for  the  absorption  of  hydrogen  gas  a  solution  of 
colloidal  palladium  with  sodium  protalbinate  as  protective 
colloid.  To  avoid  the  necessity  of  oxidizing  the  palladium 

1  Z.fiir  analytische  Chemie,  49  (1910),  729. 

~  Berichte  der  deutschen  chemischen  Gesellschaft,  43  (1910),  243. 


PROPERTIES   OF  THE   VARIOUS   GASES  183 

hydride  after  each  absorption,  they  make  use  of  the  fact  that 
hydrogen  that  has  been  absorbed  by  colloidal  palladium  is  able 
rapidly  to  reduce  organic  nitro-compounds  such  as  picric  acid. 

C6H2(NO2)3  OH  +  18  H  =  C6H2(NH2)3  OH  +  6  H2O. 

Consequently  when  sodium  picrate  is  added  in  excess  to  the 
solution  of  the  absorbent,  the  solution  will  rapidly  and  quantita- 
tively absorb  a  large  volume  of  hydrogen  gas. 

The  authors  prepare  the  reagent  by  dissolving  two  grams  of 
sodium  protalbinate  in  50  cc.  of  water,  adding  sodium  hydroxide 
in  slight  excess  and  then  slowly  adding  1.6  grams  of  palladium 
chloride  ( =  i  gram  Pd)  previously  dissolved  in  25  cc.  of  water. 
A  reddish  brown  liquid  results  which  remains  clear.  To  this  is 
added  hydrazine  hydrate  drop  by  drop.  Reduction  takes  place 
at  once.  The  solution  is  allowed  to  stand  for  three  hours  and  is 
then  placed  in  a  dialyzer  and  dialyzed  against  water  until  the 
outer  water  shows  no  further  test  for  hydrazine  hydrate  or 
sodium  chloride.  The  resulting  solution  is  concentrated  at  a 
temperature  of  68°  to  70°  and  is  then  evaporated  to  dryness  over 
concentrated  sulphuric  acid  in  a  vacuum.  Black,  glistening 
plates  result  which  are  soluble  in  water  without  leaving  a  resi- 
due.1 For  the  absorption  of  hydrogen,  the  authors  dissolve  2.74 
grams  of  sodium  picrate  and  2.44  grams  of  61.33%  colloidal 
palladium  (Kalle)  in  water  and  dilute  the  solution  to  130  cc. 
The  reagent  may  be  used  in  a  Hempel  simple  gas  pipette. 
Analyses  made  with  this  absorbent  show  that  hydrogen  is  com- 
pletely removed  from  a  gas  sample  in  from  10  to  30  minutes  and 
that  hydrogen  may  quantitatively  be  separated  from  nitrogen 
and  saturated  gaseous  hydrocarbons.  If  ^oxygen  is  present  with 
the  hydrogen  in  the  gas  mixture  the  oxygen  should  first  be  re- 
moved by  means  of  alkaline  pyrogallol  or  other  suitable  ab- 
sorbent because  of  the  fact  that  colloidal  palladium  will  cause 
oxygen  and  hydrogen  to  unite.  Carbon  monoxide  is  not  ab- 

1  Colloidal  palladium  in  solid  form  prepared  according  to  the  above  procedure 
may  be  obtained  from  Kalle  and  Company,  Biebrich  am  Rhein,  Germany. 


184  GAS  ANALYSIS 

sorbed  by  the  reagent,  but  the  gas  seems  to  retard  the  absorption 
of  hydrogen  by  colloidal  palladium.  For  this  reason  the  authors 
recommend  that  carbon  monoxide  be  first  removed  by  ammonia- 
cal  cuprous  chloride  and  that  the  hydrogen  in  the  residue  be 
then  absorbed  by  the  palladium  solution. 

Brunck  has  made  a  careful  examination  of  the  method  of 
Paal  and  Hartmann  with  a  view  to  ascertaining  whether  it  is 
adapted  to  technical  practice.1  He  finds  that  the  procedure 
gives  very  satisfactory  results  and  states  that  he  regards  it  as 
even  more  accurate  than  the  combustion  method  for  the  deter- 
mination of  hydrogen.  Brunck  employs  a  Hempel  gas  burette 
with  water  as  the  confining  liquid  and  a  Hempel  simple  absorp- 
tion pipette  for  solid  and  liquid  reagents,  see  page  55,  for  hold- 
ing the  absorbent.  The  removal  of  the  hydrogen  is  more  rapid 
if  the  pipette  is  shaken  or  if  it  is  filled  with  small  glass  balls  of 
from  5  to  7  mm.  diameter.  The  size  of  these  glass  balls  should 
be  such  that  when  the  pipette  is  filled  with  them  it  will  still  be 
able  to  hold  from  80  to  90  cc.  of  gas.  The  absorbent  is  prepared 
either  by  dissolving  two  grams  of  colloidal  palladium  2  in  water 
and  adding  5  grams  of  picric  acid  that  has  been  neutralized  with 
sodium  hydroxide  and  diluting  the  whole  to  from  100  to  no  cc., 
or  by  dissolving  the  corresponding  amount  of  the  absorption 
mixture,  which  is  now  prepared  ready  for  use  by  Kalle  and  Com- 
pany, in  100  cc.  of  water.  This  amount  of  the  reagent  has  a 
theoretical  absorbing  power  of  4369  cc.  of  hydrogen  measured 
under  standard  conditions.  Relatively  small  amounts  of  hydro- 
gen, 10  to  20  cc.,  are  absorbed  in  about  5  minutes;  somewhat 
larger  amounts  in  about  ten  minutes.  When,  however,  the  gas 
mixture  contains  50  per  cent  or  more  of  hydrogen,  the  gas  should 
be  passed  over  into  the  pipette  and  allowed  to  stand  for  5 
minutes,  then  drawn  back  into  the  burette  so  that  the  gas  balls 
in  the  pipette  again  become  moistened  with  the  absorbent,  and 

1  Chemiker-Zeitung,  34  (igio),  1313. 

2  Brunck  states  that  the  present  market  price  of  this  substance  in  Germany  is  10 
Marks  a  gram. 


PROPERTIES  OF  THE  VARIOUS   GASES  185 

then  passed  back  again  into  the  pipette.  This  should  be  con- 
tinued until  no  further  diminution  of  gas  volume  is  noted.  The 
removal  of  hydrogen  from  100  cc.  of  a  gas  mixture  containing  a 
high  per  cent  of  this  gas  takes  from  20  to  30  minutes.  This 
method  is  naturally  best  applicable  to  the  determination  of 
hydrogen  in  the  presence  of  nitrogen  or  of  methane,  or  of  both 
of  these  gases.  A  series  of  analyses  of  a  mixture  of  hydrogen 
and  nitrogen  shows  that  the  determination  of  hydrogen  is 
accurate  to  within  o.i  cc.  which  falls  well  within  the  limits  of 
experimental  error  when  the  sample  is  not  greater  than  100  cc. 
and  the  analysis  is  made  over  water. 

The  high  cost  of  the  reagent  would  constitute  a  serious  objec- 
tion to  its  employment  in  technical  practice  were  it  not  easily 
possible  to  regenerate  it.  This  may  be  done  1  as  follows:  The 
reagent  is  transferred  from  the  gas  pipette  to  a  flask  and 
the  pipette  is  rinsed  with  water  which  is  added  to  the  liquid  in 
the  flask.  Very  dilute  sulphuric  acid  is  added  drop  by  drop  to  the 
solution  so  long  as  a  precipitate  results.  A  large  excess  of  sul- 
phuric acid  is  to  be  avoided  because  it  might  cause  the  colloidal 
palladium  to  change  to  palladium  sulphate  through  action  of 
atmospheric  oxygen.  The  precipitate  which  contains  palladium, 
free  protalbinic  acid  and  unused  picric  acid  is  washed  with 
water  which,  while  it  may  dissolve  some  of  the  acids,  carries  no 
palladium  into  solution.  The  precipitate  is  then  suspended  in  a 
small  amount  of  water  and  is  dissolved  by  adding  sodium  hydrox- 
ide drop  by  drop.  Fresh  sodium  picrate  is  then  added,  and  the 
solution  diluted  with  water  to  its  original  volume  of  about  100 
cc.  It  is  now  again  ready  for  use. 

In  a  recent  article  2  Hempel  states  that  the  solution  of  col- 
loidal palladium  foams  very  strongly  anci  that  this  necessitates 
waiting  a  considerable  length  of  time  after  the  absorption  of  hy- 
drogen is  complete  until  the  foam  has  disappeared  and  the  gas 
residue  can  be  transferred  to  the  burette  for  measurement.  He 

1  Paal,  Chemiker-Zeitung,  34  (1910),  1332. 
2Z./.  angew.  Chem.,  25  (1912),  1841. 


i86  GAS  ANALYSIS 

cites  experiments  carried  on  by  Petschek  which  show  that  the 
absorbing  liquid  prepared  according  to  the  method  of  Paal  and 
Hartmann  slowly  loses  its  absorbing  power  even  when  it  stands 
in  the  dark.  For  this  reason  Hempel  recommends  that  the  re- 
agent be  used  over  mercury  in  an  absorption  pipette  and  that 
small  quantities  of  the  freshly  prepared  absorbing  liquid  be 
employed  for  the  analyses. 

Determination  of  Hydrogen  by  Explosion. — Hydrogen  may 
be  determined  by  mixing  the  gas  with  not  more  than  four  times 
its  volume  1  of  pure  oxygen,  exploding  the  mixture  and  measur- 
ing the  contraction  of  the  gas  volume.  The  gas  mixture  may 
be  exploded  over  mercury  in  a  eudiometer  such  as  Bunsen  em- 
ployed, or  the  explosion  pipette  described  on  page  141  may  be 
used.  The  volume  of  hydrogen  that  was  present  is  equal  to  § 
of  the  observed  contraction 

2  H2  +  O2  =2  H2O. 

If  air  is  employed  instead  of  oxygen,  it  should  be  borne  in  mind 
that  a  mixture  of  hydrogen  and  air  that  contains  less  than  10 
per  cent  or  more  than  63  per  cent  of  hydrogen  is  not  explosive  2 
and  that  the  most  accurate  results  will  be  obtained  when  the 
ratio  of  the  volume  of  the  gas  that  does  not  enter  into  the  ex- 
plosion to  that  of  the  hydrogen  and  oxygen  uniting  is  about  4 
to  i.  The  determination  of  hydrogen  by  explosion  with  oxygen 
or  air  is  not  well  suited  to  technical  gas  analysis  because  the  re- 
action is  so  violent  as  to  necessitate  the  use  of  only  a  small  vol- 
ume of  hydrogen  with  consequent  decrease  in  the  accuracy  of 
the  results.  Moreover,  as  Misteli  points  out 3  small  amounts 
of  hydrogen  escape  combustion  in  the  determination  of  the 
gas  by  explosion.  Furthermore  when  nitrogen  is  present  there 
is  possibility  of  error  through  the  formation  of  oxides  of 
nitrogen. 

1  Bunsen,  Gasometrische  Methoden,  2d  ed.,  p.  119. 

2  Teclu,  Journal  fur  praktische  Chemie,  75  (1907),  212. 

3  J.fiir  Gasbeleuchtung,  48  (1905),  802. 


PROPERTIES  OF  THE  VARIOUS   GASES  187 

Determination  of  Hydrogen  with  Combustion  Pipette.  — 

Hydrogen  may  be  determined  with  a  high  degree  of  accuracy 
by  the  combustion  method  described  by  the  author  and  C.  G. 
Hopkins.1  In  this  method  the  hydrogen  may  first  be  introduced 
into  the  combustion  pipette  (see  Fig.  74)  and  then  burned  with 
a  mixture  of  equal  parts  of  oxygen  and  air,  or  pure  oxygen  may 
be  introduced  into  the  pipette  and  the  hydrogen  be  then  passed 
in.  Either  procedure  gives  equally  accurate  results.  In  the 
first  form  of  manipulation  a  sample  (about  100  cc.)  of  the  hydro- 
gen under  examination  is  measured  off  in  a  burette  and  is  then 
passed  over  into  the  combustion  pipette.  A  mixture  of  about 
equal  parts  of  oxygen  and  air  containing  an  amount  of  oxygen 
more  than  sufficient  for  the  combustion  of  the  hydrogen  is  meas- 
ured off  in  the  burette,  and  the  burette  and  pipette  are  then 
connected  by  a  bent  glass  capillary  tube  in  the  usual  manner 
(see  Fig.  75).  The  platinum  spiral  is  heated  to  dull  redness  by 
means  of  an  electric  current,  and  the  mixture  of  air  and  oxygen 
is  slowly  passed  over  from  the  burette  into  the  pipette.  During 
the  combustion  the  current  should  be  regulated  by  means  of  the 
rheostat  so  that  the  spiral  is  at  no  time  heated  beyond  dull  red- 
ness. The  combustion  of  the  hydrogen  is  complete  almost  as 
soon  as  sufficient  oxygen  has  been  introduced.  When  nearly 
all  of  the  mixture  of  air  and  oxygen  is  passed  into  the  pipette, 
the  pinchcock  at  the  top  of  the  burette  is  closed  and  the  spiral 
is  kept  at  dull  redness  for  sixty  seconds.  The  current  is  then 
turned  off,  the  pipette  is  allowed  to  cool  and  the  residual  gas 
is  passed  back  into  the  burette  and  measured.  In  this  form 
of  the  method  the  hydrogen  is  burned  with  a  mixture  of  oxygen 
and  air  because  if  pure  oxygen  were  used,  the  contraction  in 
the  gas  volume  in  the  pipette  before  an  excess  of  oxygen  is  in- 
troduced would  cause  the  mercury  in  the  pipette  to  rise  and 
submerge  the  platinum  spiral.  The  results  of  a  series  of  de- 
terminations of  hydrogen  made  by  this  method  are  given  in  the 
following  table: 

1  Jour.  Am.  Chem.  Soc.,  21  (1899),  398. 


i88 


GAS  ANALYSIS 


I 

cc. 

II 

cc. 

III 
cc. 

IV 

cc. 

V 
cc. 

VI 

cc. 

VII 
cc. 

VIII 
cc. 

Hydrogen  taken 

99.6 

IOO.O 

98.6 

99.8 

99.4 

95-35 

97-5 

5I-I5 

Oxygen  and  air 

added 

99.6 

99-95 

99.9 

IOO.O 

99.1 

96.6 

99-75 

48.95 

Total    .      . 

199.2 

199-95 

198.5 

199.8 

198.5 

I9J-95 

197-25 

IOO.  IO 

Residue  after 

combustion    . 

50.0 

50.1 

50.8 

50.55 

49-7 

49.1 

51.2 

23-4 

Contraction 

149.2 

149.85 

147-7 

149-25 

148.8 

142.85 

146.05 

76.7 

Equivalent  to 

hydrogen 

99-47 

99-9 

98.47 

99-5 

99-3 

95-23 

97-37 

51-13 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Hydrogen 

found 

99-9 

99  9 

99  9 

99  7 

99  9 

99  9 

99-9 

IOO.O 

In  the  other  style  of  manipulation  a  measured  amount  (about 
100  cc.)  of  oxygen  is  passed  into  the  combustion  pipette,  the 
sample  of  hydrogen  under  analysis  (about  100  cc.)  is  measured  off 
in  the  burette,  the  burette  and  pipette  are  connected,  the  spiral 
is  brought  to  dull  redness  and  the  hydrogen  is  slowly  passed  into 
the  pipette  until  the  following  confining  liquid  reaches  the  con- 
necting capillary.  In  either  manner  of  manipulation,  the  confin- 
ing liquid,  water  or  mercury,  should  not  be  driven  further  than 
this  because  if  it  were  to  come  in  contact  with  the  hot  part  of 
the  pipette  directly  over  the  platinum  spiral  the  glass  would 
probably  crack.  To  insure  the  complete  transferral  of  the  hy- 
drogen from  the  burette  into  the  pipette  the  level-tube  of  the 
burette  is  now  lowered  and  about  25  cc.  of  gas  is  drawn  back 
into  it  from  the  pipette.  This  is  then  driven  over  again  into 
the  pipette  and  the  procedure  is  once  more  repeated.  The 
spiral  is  kept  at  dull  redness  for  sixty  seconds  longer,  the  pipette 
is  then  allowed  to  cool  and  the  gas  is  passed  back  into  the  bu- 
rette and  measured. 

The  Absorption  of  Hydrogen  by  Palladium-black  (Hem- 
pel). — The  classic  method  devised  by  Hempel  for  the  separation 
of  hydrogen  from  ethylene,  nitrogen  and  gases  of  the  paraffin 
series,  in  which  the  hydrogen  without  being  mixed  with  oxygen 


PROPERTIES   OF  THE   VARIOUS   GASES  189 

is  directly  absorbed  by  palladium-black  at  a  temperature  of 
about  1 00°,  is  one  of  the  most  accurate  and  satisfactory  proce- 
dures for  the  determination  of  this  gas  that  has  ever  been  de- 
vised. The  arrangement  of  the  apparatus  is  shown  in  Fig.  79. 
The  palladium-black  is  first  rendered  active  by  superficially 
oxidizing  it  by  heating  it  to  redness  on  the  lid  of  a  platinum 
crucible  and  slowly  raising  the  crucible  lid  out  of  the  flame. 
About  four  grams  of  this  palladium-black  is  placed  in  the  tube  H 
which  is  made  of  soft  glass  tubing.  This  tube  has  an  internal 
diameter  of  4  mm.  and  is  10  cm.  high.  To  the  upper  ends  of  H 
are  connected  the  two  bent  capillary  tubes  D  and  E.  E  is  con- 
nected with  a  gas  pipette  C  that  contains  water,  and  that  is  used 
simply  to  render  possible  the  passage  of  the  gas  back  and  forth 
through  the  palladium-black.  The  other  capillary  tube  D  is 
joined  to  the  burette  A  that  contains  the  gas  mixture  in  which 
free  hydrogen  is  to  be  determined.  Gases  other  than  hydrogen, 
nitrogen,  ethylene,  and  methane  and  its  homologues  must  pre- 
viously be  removed  by  absorption.  There  is  now  brought  up  un- 
der the  U-tube  H  a  beaker  containing  water  at  a  temperature  of 
about  100°.  The  point  at  which  the  water  stands  in  the  capillary 
of  the  pipette  is  noted,  the  pinchcock  P  is  then  opened  and  the 
gas  mixture  passed  three  times  back  and  forth  through  the  pal- 
ladium tube  by  raising  and  lowering  the  level-tube  B.  The 
beaker  of  hot  water  is  now  replaced  by  one  containing  water 
of  the  temperature  of  the  room  and  the  gas  residue  is  twice 
passed  back  and  forth  through  this  tube  to  cool  it.  The  gas  is 
then  drawn  back  into  the  burette  until  the  water  stands  at  the 
original  point  in  the  capillary  of  the  pipette.  P  is  then  closed 
and  the  residual  gas  volume  in  the  burette  is  measured.  The 
difference  between  the  measurements  made  before  and  after 
the  absorption  is  equal  to  the  hydrogen  in  the  gas  mixture  plus 
the  volume  of  the  oxygen  in  the  air  that  was  originally  inclosed 
in  the  U-tube  when  the  apparatus  was  put  together. 

This  volume  of  oxygen  in  the  U-tube  may  accurately  be  de- 
termined once  and  for  all  in  the  following  manner.    Somewhat 


190 


GAS  ANALYSIS 


FIG.  79 


PROPERTIES  OF  THE  VARIOUS   GASES  191 

more  than  100  cc.  of  air  is  drawn  into  a  phosphorus  pipette 
(Fig.  35)  and  allowed  to  stand  until  the  oxygen  has  been  re- 
moved and  the  fumes  of  phosphorus  pentoxide  have  been  ab- 
sorbed. The  pipette  is  connected  with  a  gas  burette  and  the 
nitrogen  in  the  pipette  is  passed  over  into  the  burette  and  is 
measured.  The  pipette  is  now  connected  with  one  end  of  the 
freshly  rilled  palladium  tube  which  itself  is  immersed  in  a  beaker 
of  water  of  the  temperature  of  the  room.  The  other  end  of  the 
U-tube  is  connected  with  the  burette  that  contains  the  nitrogen. 
The  level-tube  of  the  burette  is  then  raised  and  the  nitrogen 
is  driven  over  into  the  pipette  until  the  confining  liquid  reaches 
the  top  of  the  burette.  The  pinchcock  is  then  closed  and  the 
gas  is  allowed  to  stand  in  the  phosphorus  pipette  for  about  three 
minutes.  The  gas  is  then  drawn  back  into  the  burette  and 
again  passed  over  into  the  pipette.  The  residual  nitrogen  is  then 
drawn  back  into  the  burette  and  its  volume  is  read.  The  differ- 
ence between  this  and  the  first  reading  gives  the  volume  of  oxy- 
gen that  was  originally  in  the  palladium  tube.  The  palladium- 
black  is  regenerated  from  time  to  time  by  heating  it  on  the  lid 
of  a  platinum  crucible  in  the  manner  above  described. 

The  Fractional  Combustion  of  Hydrogen.  —  In  the  analysis 
of  those  mixtures  of  gases  that  most  commonly  occur  in  technical 
practice,  the  determination  of  the  majority  of  the  constituents 
may  be  accomplished  by  the  absorption  of  the  gases  by  liquid 
reagents  or  by  solid  reagents  immersed  in  liquids.  This  method 
is,  however,  not  applicable  to  the  determination  of  the  gases  of 
the  paraffin  series  nor  has  it  been  possible  until  recently  (see 
page  182)  to  remove  hydrogen  by  means  of  a  liquid  absorbent. 
In  gas  mixtures  or  gas  residues  that  contain  hydrogen  and  only 
one  member  of  the  paraffin  series,  both  gases  may  satisfactorily 
be  determined  by  burning  the  gases  simultaneously  in  the  com- 
bustion pipette  shown  in  Fig.  74,  measuring  the  contraction,  and 
ascertaining  the  volume  of  carbon  dioxide  that  has  been  formed. 
The  analysis  of  such  a  mixture  of  combustible  gases  by  the  ex- 
plosion method  (see  page  141)  is  not  as  accurate  as  that  by  the 


192  GAS  ANALYSIS 

combustion  method  just  referred  to.  Particularly  is  this  true 
of  the  simultaneous  determination  of  hydrogen  and  methane  in 
gas  residues  that  contain  large  amounts  of  these  two  gases,  for 
in  such  case  only  a  small  portion  of  the  combustible  residue  can 
safely  be  exploded  and  consequently  any  experimental  error  is 
multiplied  five-  to  eight-fold  when  the  results  are  calculated  for 
the  whole  of  the  gas  residue.  Moreover,  if  two  or  more  hydro- 
carbons of  the  same  group  are  present  with  the  hydrogen,  the 
gases  cannot  be  determined  by  any  combustion  or  explosion 
method  in  which  all  of  the  combustible  gases  are  simultaneously 
burned  (see  page  131).  For  these  reasons  a  satisfactory  method 
for  the  fractional  combustion  of  mixtures  of  hydrogen  and 
hydrocarbons  of  the  paraffin  group,  a  method  by  means  of 
which  the  hydrogen  gas  alone  may  be  burned  without  oxida- 
tion of  the  hydrocarbons,  has  long  been  sought  and  many  differ- 
ent procedures  have  been  suggested. 

Fractional  Combustion  of  Hydrogen  with  Platinum  or  Pal- 
ladium Asbestos.  —  The  first  method  of  fractional  combustion 
was  proposed  by  Henry  1  who  found  that  he  could  remove  hydro- 
gen and  carbon  monoxide  from  the  mixture  of  these  two  gases 
with  methane  and  nitrogen  by  passing  the  gases  over  platinum 
sponge  heated  to  177°.  Somewhat  later  Coquillion  discovered  2 
that  hydrogen  and  methane,  when  mixed  with  air,  could  be 
burned  by  passing  the  gases  over  a  spiral  of  metallic  palladium 
heated  to  bright  redness  by  an  electric  current.  In  1878  Bunte 
described  3  a  method  for  the  combustion  of  hydrogen  in  which 
the  mixture  of  the  gas  with  air  or  oxygen  is  passed  over  palladium 
that  is  heated  externally  to  the  desired  temperature  by  means  of 
a  small  flame.  It  was  afterward  found  that  if  the  temperature 
to  which  the  metallic  palladium  is  heated  is  kept  below  a  certain 
point,  methane  does  not  burn  and  that  consequently  the  deter- 
mination of  hydrogen  when  admixed  with  methane  may  be 

1  Annals  of  Philosophy,  25  (1825),  428. 

2Compt.  rend.,  83  (1876),  799;  84  (1877),  1503;  85  (1878),  1106. 

8  Berichte  der  deutschen-chemischen  Gesellschaft,  n  (1878),  1123. 


PROPERTIES   OF  THE   VARIOUS   GASES  193 

effected  in  this  manner.  Other  contact  substances  for  the  frac- 
tional combustion  of  hydrogen  have  been  suggested.1  In  later 
articles  upon  this  subject,  different  authors  called  attention  to 
the  fact  that  some  or  all  of  the  methane  will  burn  with  the 
hydrogen  if  the  temperature  is  allowed  to  rise  too  high,  but  con- 
siderable difference  of  opinion  existed  as  to  the  temperature  to 
which  the  catalytic  substance  might  be  heated  without  causing 
oxidation  of  the  methane.  In  fact,  in  many  of  the  published 
methods,  the  authors  contented  themselves  with  a  descrip- 
tion of  some  arbitrary  method  of  heating  the  tube  containing 
the  catalyzer  and  evidently  assumed  that  when  the  condi- 
tions that  they  laid  down  are  followed,  no  methane  will  be 
burned.  For  example,  in  the  instructions  given  by  different 
writers  concerning  the  heating  of  the  glass  tube  containing 
palladium  wire  or  palladium  asbestos  are  to  be  found  such  state- 
ments as  the  following:  "the  heating  of  a  tube  should  be  gentle 
and  in  no  case  should  it  cause  a  visible  glow:"  "the  tube  should 
be  heated  to  such  a  temperature  that  it  can  be  touched  for  a 
moment  without  burning  the  finger:"  "the  tube  should  be 
heated  to  such  a  temperature  as  will  just  be  sufficient  to  cause 
the  potassium  or  sodium  in  the  glass  to  color  the  Bunsen  flame." 
It  is  true  that  the  last  statement  was  made  by  a  writer  who 
ascertained  by  means  of  a  thermocouple  that  the  difficultly 
fusible  glass  tubing  that  he  was  using  began  to  color  the  Bunsen 
flame  at  a  temperature  lying  between  550°  and  600°,  but  his 
directions  would  be  of  dubious  value  to  another  operator  using 
a  different  sample  of  hard  glass.  Moreover,  as  Richardt  has 
pointed  out,2  finely  divided  contact  substances  such  as  palla- 
dium asbestos,  platinum  asbestos  or  palladium  sponge  are  poor 

1  Palladium  asbestos,  Winkler,  Anleit.  z.  chem.  Unters.  der  Industrie-Case,  part  2, 
p.  258. 

Palladium  sponge,  Hempel,  Berichte  der  deutschen  chemischen  Gesettschaft,  12 
(1879),  1006. 

Platinum  asbestos,  Kopfer,  Berichte  der  deutschen  chemischen  Gesettschaft,  9  (1876), 

1377- 

2Z./.  anorg.  Chem.,  38  (1904),  65. 


194  GAS  ANALYSIS 

heat-conductors,  and  for  this  reason  the  heat  developed  by  the 
combustion  of  tjie  gases  within  the  tube  may  locally  raise  the 
catalyzer  to  a  temperature  at  which  methane  will  burn,  even 
when  the  external  heating  of  the  tube  is  very  carefully  regulated. 
The  observation  of  Winkler 1  that  even  when  the  glass  capillary 
tube  containing  palladium  asbestos  is  very  carefully  heated  by 
a  small  gas  flame  "the  end  of  the  asbestos  thread  against  which 
the  entering  current  of  gas  impinges  is  heated  to  a  bright  glow, 
and  that  this  glow  is  frequently  again  seen  when  the  gas  sample 
is  passed  back  into  the  burette"  is  one  that  is  familiar  to  all  who 
have  used  this  method  of  fractional  combustion. 

To  ascertain  the  temperature  at  which  methane,  when  mixed 
with  air,  will  be  oxidized  upon  passage  over  a  catalytic  agent 
Richardt 2  passed  the  gas  mixture  over  palladium  wire  that  was 
placed  in  a  capillary  tube  which  was  heated  from  the  outside  by 
a  small  flame.  He  employed  palladium  wire  instead  of  palladium 
asbestos  because  the  compact  metal,  having  high  heat  conduc- 
tivity, rendered  it  possible  to  avoid  local  superheating.  He 
found  that  methane  was  oxidized  to  some  extent  at  a  tempera- 
ture but  slightly  above  450°  and  that  it  rapidly  burned  at 
temperatures  above  700°.  From  these  measurements  it  is 
evident  that  if  the  catalytic  substance  is  heated  to  a  dull  red 
glow  that  is  visible  in  daylight,  which  according  to  Richardt 
corresponds  to  a  temperature  from  750°  to  800°,  combustion  of 
some  of  the  methane  will  undoubtedly  result. 

Results  confirmatory  of  the  statements  of  Richardt  were  later 
obtained  by  Denham  3  who  found  that  the  temperature  of  com- 
bustion of  practically  pure  methane  and  oxygen  when  the  gas 
mixture  is  passed  through  a  tube  containing  palladium  asbestos 
lies  between  514°  and  546°. 

Brunck  maintains  4  that  the  results  obtained  in  the  fractional 

1  Lehrbuch  der  technischen  Gasandyse,  1901,  168. 

2  Loc.  cit. 

3/.  Soc.  Chem.  Ind.,  24  (1905),  1202. 
*Z,f.  angew.  Chem.,  16  (1903),  695. 


PROPERTIES   OF  THE   VARIOUS   GASES  195 

combustion  of  hydrogen  by  means  of  palladium  asbestos  are 
accurate  even  when  the  asbestos  thread  visibly  glows  during  the 
passage  of  the  gas  mixture,  but  even  his  own  confirmatory 
analyses  show  that  with  slight  elevation  of  the  temperature  of 
the  capillary  tube,  some  methane  is  oxidized.  If  the  palladium 
asbestos  glows  during  the  passage  of  the  gas  its  temperature  is 
undoubtedly  considerably  above  500°.  With  this  fact  in  mind 
it  is  difficult  to  reconcile  the  statements  of  Brunck  with  the 
experimental  results  of  Nesmjelow  1  which  appear  to  demon- 
strate that  when  a  mixture  of  hydrogen,  methane  and  air  is 
passed  through  a  capillary  tube  that  contains  palladium  asbestos 
an  appreciable  amount  of  methane  is  oxidized  at  150°.  It  is 
certainly  the  case  that  when  the  fractional  combustion  of  hydro- 
gen by  means  of  palladium  asbestos  is  carried  out  in  the  manner 
prescribed  in  almost  all  of  the  various  descriptions  of  the  method, 
the  temperature  of  150°  will  be  greatly  exceeded,  particularly 
when  a  porous  catalyzer  is  employed. 

In  a  recent  review  2  of  this  method  Hempel  finds  that  hydrogen 
may  be  determined  with  accuracy  in  the  presence  of  methane 
and  ethane  if  the  palladium  asbestos  does  not  glow  during  the 
analysis,  and  if  the  temperature  of  the  capillary  itself  does  not 
rise  appreciably  above  400°.  He  states  that  this  may  be  accom- 
plished by  heating  the  capillary  in  a  certain  manner,  which  he 
describes,  and  by  passing  the  gas  mixture  very  slowly  through 

1  Z.f.  analytische  Chemie,  48  (1909),  232. 

In  this  article  Nesmjelow  gives  the  following  directions  for  the  preparation  of 
palladium  asbestos: 

Dissolve  three  grams  of  sodium  palladious  chloride  in  as  small  an  amount  of  water 
as  possible,  add  three  cc.  of  a  cold,  saturated  solution  of  sodium  formate,  and  then 
sodium  carbonate  to  strong  alkaline  reaction.  Place  in  the  solution  one  gram  of 
long-fibered,  soft  asbestos  which  will  absorb  practically  all  of  the  liquid.  Dry  the 
fiber  on  the  water-bath.  Metallic  palladium  will  hereupon  separate  evenly  on  the 
asbestos  in  a  black,  finely  divided  form: 

Na2PdCl4  +  HCOONa  =3  NaCl  +  HC1  +  C02  +  Pd. 

After  complete  drying  on  the  water-bath,  the  asbestos  is  softened  with  water,  and 
then  is  placed  in  a  funnel  and  washed  with  warm  water  until  the  adhering  salts  are 
removed.  It  is  then  dried  and  kept  in  stoppered  glass  bottles. 

2  Z.f.  angew.  Chetn.,  25  (1912),  1841. 


196  GAS  ANALYSIS 

the  tube,  and  that  if  these  directions  are  followed  with  the  greatest 
care  the  method  gives  agreeing  results.  These  statements  by 
Hempel  serve  to  accentuate  the  uncertainty  inherent  in  the 
fractional  combustion  of  hydrogen  by  means  of  a  catalytic  sub- 
stance that  is  heated  with  a  free  flame,  and  they  render  it  evident 
that  slight  variations  in  the  procedure  may  easily  give  rise  to 
errors  of  considerable  magnitude. 

A  much  more  satisfactory  procedure  for  the  fractional  com- 
bustion of  hydrogen  is  Hempel's  method  of  burning  the  hydrogen 
by  means  of  palladium  black  that  is  kept  at  a  temperature  below 
100°,  or  that  of  Jager  in  which  the  fractional  combustion  of  the 
hydrogen  is  accomplished  by  passing  the  gas  over  copper  oxide 
at  a  temperature  of  250°. 

Fractional  Combustion  of  Hydrogen  with  Palladium  Black 
(Hempel) .  —  The  method  is  based  upon  the  fact  that  if  a  mix- 
ture of  hydrogen,  methane  and  air,  oxygen  being  present  in  ex- 
cess, is  passed  over  palladium  black  at  a  temperature  not  above 
100°,  hydrogen  alone  is  burned. 

Finely  divided  palladium  is  prepared  for  use  in  this  method  by 
heating  it  to  redness  upon  the  lid  of  a  platinum  crucible  and 
gradually  removing  it  from  the  flame  so  that  it  will  cool  slowly. 
This  covers  the  metal  with  a  very  thin  layer  of  palladious  oxide. 

About  0.5  gram  of  this  palla- 
dium black  is  placed  in  a  small 
U-shaped  glass  tube  (Fig.  80). 
This  tube  is  connected  by  short 
pieces  of  rubber  tubing  with  the 
^^3^  bent  capillary  tubes  EE  one  of 

pjG  8o  which   is   joined  to  a  gas  bu- 

rette while   the   other  is  con- 
nected with  a  simple  gas  pipette  filled  with  water. 

From  15  to  20  cc.  of  the  mixture  of  hydrogen  and  methane  is 
brought  into  a  Hempel  burette  and  accurately  measured.  There 
is  then  drawn  into  the  burette  such  an  amount  of  air  as  will 
insure  the  presence  of  more  than  enough  oxygen  to  unite  with 


PROPERTIES  OF  THE  VARIOUS   GASES 


197 


the  hydrogen  in  the  gas  mixture.  The  total  volume  of  the  gas  is 
now  measured.  The  right  hand  capillary  E  having  been  con- 
nected with  a  gas  pipette  filled  with  water,  the  left  hand  capil- 
lary is  now  joined  to  the  burette  containing  the  gas  sample  and 
air,  and  a  beaker  containing  water  of  a  temperature  of  from  60° 
to  80°  is  brought  up  under  the  U-shaped  tube  and  set  at  such  a 
height  that  the  water  stands  just  below  the  lower  ends  of  the 
rubber  connections.  The  gas  mixture  in  the  burette  is  now 
passed  very  slowly  through  the  palladium  tube  into  the  pipette. 
With  too  rapid  a  passage  of  the  gas  mixture  over  the  palladium 
black  the  heat  developed  by  the  combustion  of  hydrogen  may 
raise  the  palladium  to  a  temperature  at  which  methane  will  begin 
to  burn.  With  reasonable  care,  however,  the  temperature  of  the 
U-tube  and  of  its  contents  may  easily  be  kept  below  100°  and  the 
combustion  of  methane  entirely  avoided.  The  gas  mixture  is 
passed  backward  and  forward  from  burette  to  pipette  until  no 
further  decrease  in  the  volume  of  the  gas  is  observed.  The 
beaker  of  warm  water  is  then  removed  and  is  replaced  by  a 
beaker  filled  with  water  of  the  temperature  of  the  room.  When 
the  residual  gas  has  in  this  manner  been  brought  to  room  tem- 
perature, the  diminution  of  the  volume  of  the  gas  is  read.  The 
volume  of  hydrogen  in  the  sample  is  equal  to  two-thirds  of  the 
contraction  noted.  Hempel  gives  the  following  results  as  con- 
firmatory of  the  accuracy  of  this  method. 


COMPOSITION  OF  THE  GAS  MIXTURE 

HYDROGEN 

Hydrogen 

Marsh-gas 

Air 

RESULTING 
CONTRACTION 

CALCULATED 

FROM  THE 

CONTRACTION 

I-  5 

12.0 

85-1 

•2.3 

i-5 

3-0 

8-3 

86.5 

4-5 

3-0 

5-i 

12.3 

86.0 

7-6 

5-o 

9-3 

7-i 

83-7 

14.1 

9-4 

13-7 

7-3 

77-5 

20.3 

13-5 

14.1 

5-4 

81.2 

21  .  2 

14.1 

14.6 

4-5 

80.6 

22.  I 

14.7 

13-1 

6.0 

80.3 

19.7 

i3-i 

198  GAS   ANALYSIS 

An  objection  that  may,  however,  be  urged  against  this  method 
is  that  only  a  portion  of  the  combustible  residue  is  employed  and 
consequently  an  experimental  error  in  the  combustion  is  multi- 
plied several  times  when  the  result  is  calculated  for  the  total 
residue. 

Fractional  Combustion  of  Hydrogen  with  Copper  Oxide 
( Jager) .  —  The  use  of  copper  oxide  for  the  determination  of 
gaseous  hydrocarbons  was  proposed  by  Fresenius  as  long  ago  as 
I864,1  and  the  method  was  afterward  further  developed  by 
Scheurer-Kestner  2  and  Stockmann.3 

Jager  was  the  first  who  proposed  the  use  of  copper  oxide  in  the 
fractional  combustion  4  of  hydrogen  in  the  presence  of  methane, 
hydrogen  being  completely  burned  when  passed  over  copper 
oxide  5  at  a  temperature  of  250°,  whereas  methane  is  not  oxidized 
at  all  under  these  conditions.  Jager  places  copper  oxide  in  a 
hard  glass  tube  6  cm.  in  length  and  one  cm.  in  external  diameter. 
One  end  of  the  tube  terminates  in  a  straight  capillary  tube  3  cm. 
long.  To  the  other  end  is  fused  a  glass  tube  4  cm.  in  length  and 
5  mm.  internal  diameter  through  which  the  fine  granular  copper 
oxide  is  introduced.  This  combustion  tube  is  connected  on  one 
side  to  a  gas  burette  and  on  the  other  to  a  Hempel  simple  gas 
pipette  containing  a  solution  of  potassium  hydroxide.  To  facili- 
tate the  control  of  the  temperature  the  combustion  tube  rests  in 
a  small  oven  of  sheet  iron  through  the  top  of  which  a  thermom- 
eter is  inserted  to  such  a  distance  that  its  bulb  rests  directly 

1  Z.f.  analytische  Chemie,  3  (1864),  339. 

2  A.  Scheurer-Kestner,  Bullet,  de  la  Societe  industriette  de  Mulhouse,  1868;  Civil- 
ingenieur,  N.  F.,  XV,  123. 

3  C.  Stockmann,  Die  Case  des  Eochofens  und  der  Siemens-Generator  en,  Ruhrort 
1876,  6. 

4  Jour.  f.  Gasbeleuchtung,  41  (1898),  764. 

5  The  oxygen  for  the  combustion  of  hydrogen  comes  from  the  solid  copper  oxide 
which  on  reduction  decreases  in  volume.     Consequently  the  results  obtained  by 
measuring  the  contraction  of  the  gas  volume  are  somewhat  too  high.    The  error  from 
this  source  is,  however,  so  very  small  that  it  may  be  entirely  disregarded.    For  ex- 
ample, in  the  determination  of  hydrogen,  the  correction  would  be  0.00047  cc.  for 
each  cubic  centimeter  of  the  gas. 


PROPERTIES  OF  THE  VARIOUS   GASES  199 

against  the  combustion  tube.  The  oven  is  heated  from  below  by 
a  single  gas  burner.  In  the  fractional  combustion  of  hydrogen 
in  a  mixture  of  that  gas  with  methane  and  nitrogen  the  combus- 
tion tube  is  first  heated  to  250°,  and  the  gas  mixture  is  then 
slowly  passed  through  it  from  the  burette  into  the  pipette. 
Jager  found  that  a  double  passage  of  the  gas  through  the  tube 
usually  suffices  for  the  complete  combustion  of  the  hydrogen, 
but  the  gas  mixture  is  usually  passed  through  the  tube  a  third 
time  to  ascertain  whether  further  diminution  in  volume  takes 
place.  Since  the  oxygen  of  the  air  that  is  originally  contained 
in  the  combustion  tube  burns  with  the  hydrogen,  the  contrac- 
tion due  to  this  source  must  be  ascertained.  Jager  does  this  once 
and  for  all  by  passing  through  the  heated  combustion  tube  a 
mixture  of  known  volumes  of  hydrogen  and  nitrogen.  The 
observed  contraction  less  the  contraction  due  to  the  hydrogen 
used  gives  the  volume  of  the  oxygen  in  the  combustion  tube. 

The  method  is  distinctly  superior  to  the  fractional  combustion 
of  hydrogen  by  palladium  or  palladium  asbestos  because — 

1.  No  air  or  oxygen  is  added  to  the  combustible  gas,  which 
makes  it  possible  to  pass  the  total  gas  residue  through  the 
tube  with  consequent  gain  in  accuracy  of  the  analytical  re- 
sults : 

2.  The  temperature  at  which  the  hydrogen  burns,  250°  C.,  is 
so  easily  controlled  and  is  so  far  below  the  temperature  at  which 
methane  will  be  oxidized  as  to  render  impossible  the  combustion 
of  any  of  the  methane; 

3.  The  material  and  apparatus  are  inexpensive. 

To  avoid  the  necessity  of  determining  the  volume  of  oxy- 
gen in  the  combustion  tube  and  of  making  correction  for  it, 
v.  Knorre *  first  fills  the  tube  with  nitroge'n,  this  gas  being  passed 
into  the  combustion  tube  through  a  T-tube  that  is  introduced 
between  the  combustion  tube  and  the  pipette.  He  obtains  the 
necessary  volume  of  nitrogen  by  passing  air  into  a  phosphorus 
pipette  (page  164)  and  he  states  that  the  nitrogen  residue  from 

1  Chemiker-Zeitung,  33  (1909),  717. 


200  GAS  ANALYSIS 

100  cc.  of  air  is  amply  sufficient  to  displace  the  oxygen  in  the 
combustion  tube. 

Jager  recommended  that  the  methane  in  the  gas  residue  be 
determined,  after  the  fractional  combustion  of  hydrogen,  by 
'  raising  the  temperature  of  the  combustion  tube  to  bright  red- 
ness, passing  the  mixture  of  methane  and  nitrogen  through  the 
tube  and  ascertaining  the  volume  of  methane  by  determining 
either  the  contraction  or  the  volume  of  carbon  dioxide  formed 
in  the  combustion.  Methane,  however,  is  not  easily  burned  by 
passage  over  hot  copper  oxide  and  complete  combustion  of  the 
gas  is  effected  only  by  repeatedly  passing  it  through  the  com- 
bustion tube.  Moreover,  since  the  tube  itself  must  be  kept  at  a 
bright  red  heat  throughout  the  process,  it  frequently  softens 
and  if  a  drop  of  water  enters  it,  it  instantly  breaks.  These 
difficulties  in  the  determination  of  methane  are  avoided  by 
v.  Knorre  by  substituting  for  the  hard  glass  tube  a  tube  of 
transparent  quartz  15  cm.  long,  5  mm.  internal  diameter  and 
with  a  thickness  of  wall  of  from  0.5  to  0.75  mm. 

Ubbelohde  and  de  Castro  1  also  use  a  quartz  tube  rilled  with 
copper  oxide  which  they  heat  to  270°  for  the  combustion  of  the 
hydrogen,  and  then  to  bright  redness  (800°  to  900°)  to  burn 
the  methane  and  ethane.  In  the  latter  combustion  they  heat  the 
quartz  tube  with  a  free  flame  and  place  a  clay  trough  over  the 
tube  to  bring  the  temperature  to  the  highest  point  possible. 

Excellent  as  is  the  Jager  method  for  the  accurate  determina- 
tion of  hydrogen,  the  subsequent  combustion  of  methane  at  a 
higher  temperature  in  the  same  tube  cannot  unqualifiedly  be 
recommended.  If  hard  glass  is  used  for  the  combustion  tube, 
the  tube  must  either  be  ordered  from  a  glass  blower  or  the  chem- 
ist who  makes  his  own  simple  glass  apparatus  must  purchase 
both  small  tubing  and  capillary  tubing  of  hard  glass  for  fusion 
to  the  ends  of  the  combustion  tube  proper.  The  glass  tube  is 
also  apt  to  break  when  heated  or  when  water  is  carelessly  al- 
lowed to  enter  it  during  the  combustion.  The  quartz  tube  is 

1  /./.  Gasbeleuchtung,  54  (1911),  810. 


PROPERTIES   OF   THE   VARIOUS   GASES  201 

more  durable,  but  apparatus  of  transparent  quartz  is  fragile  and 
expensive  and,  in  this  country  at  least,  it  cannot  as  yet  readily 
be  obtained.  The  chief  objection,  however,  to  this  method 
of  determining  methane  lies  in  the  fact  that  prolonged  heating 
of  the  combustion  tube  to  a  high  temperature  and  repeated 
passage  of  the  gas  through  it  are  necessary  for  the  complete 
oxidation  of  the  methane.  Because  of  these  considerations  the 
author  deems  it  preferable  to  restrict  the  combustion  with  cop- 
per oxide  to  the  fractional  combustion  of  hydrogen,  and  to  de- 
termine the  residual  methane  by  combustion  with  oxygen  in 
the  Dennis  combustion  pipette.  JSince  the  combustion  tube  need 
be  heated  only  to  250°  if  hydrogen  alone  is  to  be  burned,  this 
modification  of  the  procedure  makes  it  possible  to  use  a  tube 
of  soft  glass  which  can  easily  be  blown  by  the  operator  himself. 
The  subsequent  determination  of  methane  by  means  of  the 
combustion  pipette  is  fully  as  accurate  as  the  combustion  with 
copper  oxide  and  is  much  more  rapid.  The  following  arrange- 
ment and  manipulation  of  apparatus  have  been  found  to  give 
very  satisfactory  results. 

The  combustion  tube  (Fig.  81)  is  made  of  soft  glass  throughout. 
It  consists  of  a  piece  of  glass  tubing  H,  7  cm.  long,  12  mm.  ex- 
ternal diameter,  and  one  mm.  thickness  of  wall;  to  one  end  of 
this  tube  is  fused  a  piece  of  glass  tubing  6  cm.  long  and  7  mm. 
external  diameter;  to  the  other  end  is  fused  a  piece  of  capillary 
tubing  of  the  dimensions  used  in  the  Hempel  pipettes,  namely, 
6  mm.  external  diameter  and  one  mm.  internal  diameter,  which 
is  then  bent  at  a  right  angle  as  shown  in  the  figure.  H  is  filled 
through  the  wide  end  with  granular  copper  oxide  which  is  held 
in  place  by  a  loose  plug  of  ignited  asbestos.  Inasmuch  as  the 
temperature  of  the  copper  oxide  during  the  combustion  should 
be  kept  nearly  constant  at  270°,  the  combustion  tube  is  not 
heated  with  a  free  flame,  but  is  placed  in  a  small  air-bath,  /. 
Ubbelohde  and  de  Castro  employ  an  oven  made  of  sheet  iron 
and  lined  with  asbestos,  and  fitted  with  two  perforated  iron 
plates  for  the  even  distribution  of  the  heat.  A  device  that  is 


2O2 


GAS   ANALYSIS 


simpler  and  fully  as  satisfactory  may  be  constructed  in  the 
laboratory  from  ordinary  asbestos  board.  A  piece  of  asbestos 
board  9  cm.  wide,  30  cm.  long  and  6  mm.  thick  is  creased  at 


FIG.  8 1 

points  about  7.5  cm.  apart,  bent  into  a  four-sided  form  and  the 
ends  connected  by  shaving  one  down  to  a  sharp  edge,  splitting 
the  other,  inserting  the  narrow  edge  in  the  split  end  and  then 
thoroughly  wetting  the  asbestos  and  pressing  it  together.  The 
two  opposite  sides  of  this  box  are  notched  to  a  depth  of  about 


PROPERTIES  OF  THE  VARIOUS   GASES  203 

4.5  cm.  and  the  small  combustion  tube  rests  in  these  notches. 
The  box,  which  is  open  at  the  bottom,  rests  upon  a  piece  of 
sheet  iron  that  is  supported  on  an  iron  ring,  M .  An  asbestos 
top,  with  sides  6  cm.  high,  is  made  from  asbestos  board  in  the 
same  manner  and  opposite  sides  of  the  top  are  notched  so  that 
the  top  will  set  down  over  the  box  and  completely  close  it  ex- 
cept where  the  combustion  tube  passes  through.  A  small  open- 
ing in  the  top  made  with  a  cork  borer  serves  for  the  introduc- 
tion of  the  thermometer  T  which  is  placed  in  such  position  that 
its  bulb  rests  against  the  side  of  the  combustion  tube.  The 
air  bath  is  heated  by  a  single  Bunsen  burner,  C.  A  flame  about 
6  cm.  high  suffices  to  keep  the  interior  of  the  box  and  the  com- 
bustion tube  at  a  temperature  of  270°. 

Although  the  little  asbestos  oven  is  not  heated  higher  than 
the  comparatively  low  temperature  of  270°  throughout  the 
determination  it  is  advisable  for  the  protection  of  the  burette 
and  the  pipette  to  place  strips  of  asbestos  board,  AA,  about 
15  cm.  wide,  between  the  pipette  and  the  oven  on  the  one  side 
and  the  oven  and  the  burette  on  the  other. 

In  making  a  determination  of  hydrogen  with  this  apparatus 
the  combustion  tube  is  placed  in  position  in  the  asbestos  box, 
and  its  left-hand  end,  Fig.  81,  is  connected  with  a  water- jacketed 
Hempel  burette  that  contains  water  1  as  the  confining  liquid 
and  that  has  previously  been  filled  with  nitrogen  from  a  phos- 
phorus pipette. 

1  Mercury  may  of  course  be  used  as  the  confining  liquid,  and  a  burette  with  correc- 
tion tube  and  manometer  may  be  employed  if  great  accuracy  is  desired.  In  tech- 
nical practice,  however,  results  that  are  correct  to  within  one-tenth  of  one  per  cent 
are  usually  sufficiently  accurate,  and  inasmuch  as  the  manipulation  of  the  appara- 
tus is  more  simple  and  more  rapid  when  water  is  used  as  the  confining  liquid  in- 
stead of  mercury,  the  method  here  described  for  the*  determination,  over  water,  of 
not  only  hydrogen  but  of  methane  as  well,  has  been  worked  out  for  the  convenience  of 
the  general  analyst.  If  methane  is  the  only  hydrocarbon  that  is  present  with  the 
hydrogen,  the  two  gases  may  more  rapidly  be  determined  by  the  simultaneous  com- 
bustion of  both  with  the  combustion  pipette,  but  in  such  case  mercury  must  be  used 
as  the  confining  liquid  in  both  burette  and  pipette.  Furthermore,  if  two  members 
of  the  paraffin  group  (e.  g.,  methane  and  ethane)  are  present  in  the  gas  residue  after 
the  hydrogen  has  been  removed  by  fractional  combustion  with  copper  oxide,  the 


204  GAS  ANALYSIS 

The  pinchcock  E  at  the  top  of  the  burette  is  opened  and  the 
nitrogen  is  passed  through  the  combustion  tube  into  the  outer 
air.  This  washes  out  the  air  in  the  combustion  tube,  and  frees 
it  practically  completely  from  all  oxygen.  The  pinchcock  E 
of  the  burette  is  closed  and  a  simple  gas  pipette  filled  with  water 
up  to  the  top  of  the  rubber  connecting  tube  at  G  is  at  once  joined 
to  the  combustion  tube. 

The  rubber  tube  on  the  other  end  of  the  combustion  tube  is 
now  closed  by  the  pinchcock  F,  the  burette  is  disconnected  from 
the  bent  capillary  tube  and  about  100  cc.  of  the  gas  mixture 
under  examination,  which  should  of  course  previously  have 
been  freed  from  all  gases  except  hydrogen,  nitrogen  and  members 
of  the  paraffin  series,  is  drawn  into  the  burette  and  measured. 
While  this  is  being  done  the  heating  of  the  asbestos  oven  sur- 
rounding the  combustion  tube  is  begun  and  the  pinchcock  F  is 
opened  for  a  moment  from  time  to  time  to  relieve  the  excess 
pressure  due  to  the  expansion  of  the  nitrogen  in  the  tube.  The 
heating  is  continued  until  the  thermometer  shows  a  temperature 
of  270°  and  the  tube  is  kept  at  about  this  temperature  during  the 
combustion.  The  pinchcock  F  is  then  once  more  opened  to  bring 
the  nitrogen  in  the  combustion  tube  to  atmospheric  pressure  and 
the  burette  is  then  connected  with  the  bent  capillary  tube. 
The  pinchcocks  E,  F  and  G  are  now  opened  and  the  gas  mixture 
in  the  burette  is  slowly  passed  through  the  'combustion  tube  into 
the  water  pipette.  If  the  gas  is  passed  through  the  tube  at  the 
rate  of  about  10  cc.  per  minute  it  has  been  found  that  four  or 
five  passages  of  the  gas  will  completely  remove  the  hydrogen 
from  100  cc.  of  a  gas  mixture  that  contains  40%  of  this  gas. 

two  paraffins  can  be  determined  in  the  combustion  pipette  only  when  mercury  is 
used  as  the  confining  liquid.  In  gas  analysis,  as  in  any  other  line  of  analytical  work, 
it  should  constantly  be  borne  in  mind  that  the  refinements  of  a  method  should  be  in 
accord  with  the  accuracy  that  is  desired.  In  the  present  instance,  if  results  that  are 
correct  to  within  about  one-tenth  of  one  per  cent  meet  the  needs  of  the  case,  it  would 
involve  useless  consumption  of  time  to  employ  a  very  accurate  gas  burette  and 
to  measure  the  gases  over  mercury.  On  the  other  hand,  if  great  accuracy  is  desired, 
it  would  be  folly  to  attempt  to  attain  it  by  measurement  of  gas  volumes  over 
water. 


PROPERTIES   OF  THE  VARIOUS   GASES  205 

With  a  higher  percentage  of  hydrogen,  or  in  fact  in  any  case,  the 
gas  should  be  passed  backward  and  forward  through  the  com- 
bustion tube  until  two  successive  readings  are  the  same.  After 
the  removal  of  the  hydrogen  is  completed,  the  gas  is  drawn  back 
into  the  burette  until  the  water  in  the  capillary  of  the  pipette 
stands  just  above  K.  The  pinchcock  G  is  then  closed.  The 
temperature  of  the  combustion  tube  is  now  brought  again  to 
exactly  270°  by  raising  or  lowering  the  Bunsen  flame,  and  the 
pinchcock  E  is  closed.  The  gas  is  allowed  to  stand  in  the  burette 
for  two  minutes  to  come  to  the  temperature  of  the  surrounding 
water  and  its  volume  is  then  read.  The  contraction  in  volume 
shows  directly  the  amount  of  hydrogen. 

If  it  is  desired  to  determine  methane  in  the  gas  residue  in  the 
burette,  the  water  pipette  is  replaced  by  a  combustion  pipette 
(Fig.  74)  that  is  filled  with  water  l  and  that  contains  a  measured 
amount  of  oxygen,  about  100  cc.  The  terminals  of  the  pipette 
are  connected  with  a  source  of  electric  current,  the  current  is 
turned  on,  and  the  spiral  is  heated  to  dull  redness.  The  com- 
bustion tube  H  is  kept  at  about  270°.  The  level-bulb  of  the 
pipette  is  placed  upon  the  top  of  the  stand  S.  A  Hofmann  de- 
tachable screw  pinchcock  is  placed  upon  the  rubber  tube  that 
connects  the  burette  with  its  level-tube;  the  level- tube  of  the 
burette  is  then  brought  to  such  height  that  the  confining  liquid 
in  it  stands  but  slightly  higher  than  the  confining  liquid  in  the 
burette,  and  the  screw  pinchcock  is  now  closed.  The  level-tube 
is  placed  upon  the  top  of  another  wooden  stand  like  S.  The 
pinchcocks  E,  F,  and  G  are  opened  and  set  back  on  the  glass 
tubes.  The  screw  pinchcock  is  then  very  carefully  opened, 
and  the  gas  in  the  burette  is  very  slowly  started  over  through  H 
into  the  combustion  pipette.  When  the  water  in  the  burette 
has  risen  to  the  top  of  the  burette,  the  pinchcocks  E,  F,  and  G 
are  closed,  and  the  burette  is  disconnected  from  the  small  capil- 
lary tube  at  E.  The  burette  is  then  connected  to  a  phosphorus 
pipette  containing  nitrogen  and  a  known  volume,  from  15  to 

1  Mercury  may  of  course  be  used. 


206  GAS  ANALYSIS 

20  cc.,  of  nitrogen  is  drawn  into  the  burette.  The  burette  is 
then  disconnected  from  the  phosphorus  pipette  and  is  again 
connected  to  the  small  capillary  at  E.  Pinchcocks  E,  F,  and  G 
are  opened,  and  the  gas  forced  from  the  burette  through  the  tube 
H  into  the  combustion  pipette  as  before.  When  the  water  in 
the  burette  reaches  the  top  of  the.  burette,  pinchcock  E  is  closed, 
and  the  tube  H  is  again  brought  to  exactly  270°  C.  The  gas  in 
the  combustion  pipette  is  now  brought  to  atmospheric  pressure 
by  proper  adjustment  of  the  height  of  the  level-bulb  of  the 
pipette  and  the  pinchcock  G  is  then  closed.  The  burette  and 
the  combustion  pipette  are  disconnected  from  the  tube  H, 
and  the  burette  is  joined  directly  to  the  combustion  pipette 
by  a  capillary  tube  of  the  usual  form.  The  gas  is  drawn  from 
the  combustion  pipette  into  the  burette  and  is  then  passed 
into  a  pipette  containing  a  solution  of  potassium  hydroxide 
to  remove  carbon  dioxide.  The  residual  gas  is  now  brought 
back  into  the  burette,  and  is  again  measured.  To  ascertain 
the  volume  of  methane  in  the  sample,  add  the  volume  of  gas 
remaining  after  the  determination  of  hydrogen  to  the  sum  of 
the  oxygen  introduced  into  the  combustion  pipette  and  the 
volume  of  nitrogen  used  for  sweeping  the  residual  gas  out  of 
the  tube  H.  From  this  sum,  deduct  the  final  volume  of  the  gas 
that  remains  in  the  burette  after  the  absorption  of  the  carbon 
dioxide  formed  in  the  combustion  of  the  methane.  One-third 
of  this  result  is  the  volume  of  the  methane  in  the  gas  sample. 

NITROGEN 

Properties  of  Nitrogen.  —  Specific  gravity,  0.9701.  Weight 
of  one  liter,  1.2542  grams. 

Nitrogen  is  but  slightly  soluble  in  water,  one  volume  of 
water  absorbing,  according  to  Bunsen,  at  760  mm.  pressure 
and  f, 

0.020346  -  0.00053887  t  +  0.000011156  t2  vol.  of  nitrogen: 
or  at 


PROPERTIES  OF  THE  VARIOUS   GASES  207 

5°,  0.01794  vol. 
10°,  0.01607    " 
15°,  0.01478    " 
20°,  0.01403    " 

Otto  Pettersson  and  K.  Sonden  1  state  that  at  a  pressure  of 
760  mm.  i  liter  of  water  absorbs  from  the  air:  — 

at          o°,  19.53  cc. 

6°,  16.34  ' 
"  9.18°,  15.58  " 
"  14.10°,  14.16  " 

According  to  Carius,  one  volume  of  alcohol  takes  up  at  f, 

0.126338  —  0.000418  t  +  0.000006  t2  vol.  of  nitrogen; 

hence  at 

20°,  0.122378  vol. 

Absorption  of  Nitrogen.  —  In  the  analysis  of  gas  mixtures 
the  residue  that  cannot  be  determined  by  the  usual  absorption 
methods  or  by  combustion  was  earlier  regarded  as  consisting 
wholly  of  nitrogen  and  is  still  commonly  reported  as  such.  From 
the  researches  of  Rayleigh  and  Ramsay  we  now  know  that  this 
residue  frequently  contains,  in  addition  to  nitrogen,  one  or  more 
of  the  gases  of  the  argon  group,  which  consists  of  argon,  neon, 
krypton,  xenon  and  helium.  In  the  earlier  work  in  this  field, 
nitrogen  was  separated  from  the  gases  by  passing  the  gas  mixture 
over  hot  magnesium,  lithium,  or  a  mixture  of  magnesium  and 
calcium  oxide,  any  of  which  agents  unite  with  the  nitrogen  but 
do  not  affect  the  gases  of  the  argon  group. 

To  obtain  information  as  to  the  relative  efficiencies  of  these 
various  absorption  agents,  Hempel  placed  the  different  sub- 
stances in  hard-glass  tubes,  exhausted  these  tubes  of  air,  and 
then  introduced  an  excess  of  nitrogen.  The  tubes  were  then 
heated  to  bright  redness,  the  nitrogen  was  pumped  out  and 

1  Berichte  der  deutschen  chemischen  Gesellschaft,  22,  (1889),   1443. 


208 


GAS   ANALYSIS 


measured,  and  the  amount  of  that  gas  which  had  been  held  back 
by  each  absorbent  was  thus  determined. 
The  results  were  as  follows: — 


ABSORPTION  AGENT  EMPLOYED 

Ti!lls8 

i*iili| 
*5prs 

Number  of 
Cubic  Centi- 
meters of  Ni- 
trogen that 
was  absorbed 
in  one  hour 

i  gram  magnesium  powder,  medium  fine    . 
i  gram  lithium                        •     .  '   .     .      .  '  •  • 



M-5 
77  .  c 

i  gram  magnesium  and  5  grams  quicklime.    The 
lime  was  not  freshly  ignited     
i  gram  magnesium  and  3  grams  quicklime.    The 
lime  was  not  freshly  ignited     
i  gram  magnesium  and  8  grams  quicklime.    The 
lime  was  not  freshly  ignited     
i  gram  magnesium  and  5  grams  quicklime.    The 
lime  was  highly  ignited  shortly  before  the 
experiment          .      .          •  •     .     .     .     •  ••  . 

94-5 
86.4 

112.  O 
5O.O 
31-4 

122-5 

i   gram  magnesium,  5  grams  freshly  ignited 
lime,  and  o.i  gram  metallic  sodium    . 
i   gram  magnesium,   5  grams  freshly  ignited 
lime,  and  0.25  gram  metallic  sodium 
i   gram  magnesium,   5  grams  freshly  ignited 
lime,  and  o.n  gram  metallic  lithium 

2OI  .O 
196.0 
169.0 

287.0 
326.2 
228.0 

Ignited  lime  with  metallic  sodium  alone  absorbed  no  nitrogen 
whatever,  and  only  very  slight  absorption  is  effected  by  barium 
carbide  alone,  barium  carbide  and  potassium,  barium  fluoride 
and  sodium,  or  amorphous  boron  and  silicon.  It  is  possible  that 
the  barium  carbide  used  in  these  experiments  decomposed 
partially  when  it  was  pulverized. 

From  these  experiments  it  appeared  that,  of  the  substances 
tried,  the  best  absorbent  for  nitrogen  is  a  mixture  of  one  part  by 
weight  of  finely  powdered  magnesium  with  five  parts  by  weight 
of  freshly  ignited  lime  in  pieces  about  as  large  as  poppy  seeds, 
and  0.25  part  by  weight  of  metallic  sodium.  The  magnesium 
should  be  intimately  mixed  with  the  ignited  lime,  but  it  is 
sufficient  to  add  the  sodium  in  the  form  of  a  number  of  pieces 


PROPERTIES   OF  THE   VARIOUS   GASES  209 

each  about  half  as  large  as  a  pea.  The  layer  of  oxide  covering 
the  metallic  sodium  should  first  be  removed,  and  the  metal 
should  be  added  to  the  .mixture  just  before  using. 

The  "analytical  absorbing  power"  of  the  mixture,  based  upon 
the  amount  of  the  magnesium,  is  8.15  cc. 

Magnesium  and  lime  react  to  form  metallic  calcium.  Since 
the  above  experiments  were  made,  metallic  calcium  has  come 
upon  the  market,  and  this  may  now  be  used  directly  for  the 
removal  of  the  nitrogen,  instead  of  being  formed  within  the 
apparatus  by  the  interaction  of  magnesium  and  lime.  Metallic 
calcium  energetically  combines  with  nitrogen  forming  calcium 
nitride,  Ca3N2. 

The  researches  of  Franz  Fischer  1  have  demonstrated  that 
calcium  carbide  may  be  employed  for  the  absorption  of  nitrogen 
and  also  for  the  simultaneous  removal  of  oxygen. 

To  remove  nitrogen  from  a  mixture  of  this  gas  with  the  gases 
of  the  argon  group,  the  gas  mixture,  after  having  been  freed 
from  other  constituents,  may  be  driven  backward  and  forward  by 
means  of  mercury  through  a  heated  tube  containing  one  or 
another  of  the  above  absorbents.  Constant  raising  and  lower- 
ing of  the  mercury  level-bulbs  is,  however,  a  tedious  procedure, 
and  for  this  reason,  if  any  appreciable  amount  of  nitrogen  is  to 
be  removed,  it  will  be  found  convenient  to  employ  the  Travers  2 
modification  of  the  automatic  device  described  by  Collie.3 
By  means  of  this  apparatus  the  gases  can  automatically  be 
driven  through  the  absorption  apparatus  in  a  continuous  current. 
Fig.  82  shows  an  arrangement  of  the  apparatus  substantially 
in  the  form  recommended  by  Travers  except  that  the  bulb  reser- 
voir is  here  replaced  by  a  two-neck  Wolff  bottle  with  a  tubulure 
at  the  bottom,  and  an  iron  tube  containing  metallic  calcium  is 
used  in  place  of  a  glass  tube  filled  with  magnesium  turnings. 
A  small  Wolff  bottle,  A,  that  has  two  necks  and  a  tubulure  at 

1  Berichte  der  deutschen  chemischen  Gesellschaft,  41  (1908),  2017. 

2  Experimental  Study  of  Gases,  101. 

3  J..  Chem.  Soc.,  55  (1889),  no. 


210 


GAS  ANALYSIS 


the  bottom  is  connected  with  the  level-bulb  B  by  means  of  enam- 
elled rubber  tubing.  Into  the  two  necks  of  the  Wolff  bottle  are 
inserted,  by  means  of  rubber  stoppers,  two  glass  tubes,  one  with 
a  two-way  stopcock  and  the  other  with  a  single  stopcock.  The 
tube  D  is  bent  as  shown  in  the  figure  and  is  provided  with  a 
small  bulb  S  for  catching  any  mercury  that  may  be  carried  up 


& 

f                                                      Soda  p  n 
JGuSCuO"               Lime  haus 
afj—  n       c~      i^J  Ji-^       P        ^irjft> 

fpr— 

i  j 

Ub 

Calcium              i 
dMrfjr                                     iD-rf-fr-x 

,  frr 

~G^J'  ::H...:..."Pn\ 

FIG.  82 

through  D.  The  apparatus  may  be  connected  with  a  mercury 
air  pump  through  the  side-arm  T.  The  end  of  D  is  connected 
by  rubber  tubing,  securely  wired  m  place,  with  the  tube  E  of 
Jena  glass  containing  partially  reduced  copper  oxide,  and  the 
tube  F  containing  soda  lime  and  phosphorus  pentoxide.  The 
tube  G  is  connected  with  the  tube  H  which  is  of  iron,  and  is 
about  1.5  meter  long  and  about  2  cm.  inner  diameter.  U  is  filled 


PROPERTIES   OF  THE   VARIOUS   GASES  211 

with  pieces  of  metallic  calcium,  or,  if  this  not  available,  with 
the  mixture  of  magnesium,  freshly  ignited  lime  and  metallic 
sodium  recommended  by  Hempel.  *E  and  H  rest  in  combustion 
furnaces.  The  metallic  copper  is  used  for  the  removal  of  any 
oxygen  that  might  be  present  in  the  gas  mixture.  The  cop- 
per oxide  serves  to  oxidize  hydrogen  and  carbon  monoxide. 
Hydrogen  may  result  from  the  action  of  water  vapor  upon 
the  metallic  calcium.  The  carbon  monoxide  may  diffuse  into 
the  apparatus  through  the  hot  iron  tube.  To  avoid  this 
last  mentioned  difficulty  Franz  Fischer  and  Hahnel 1  suggest 
that  the  iron  tube  be  surrounded  by  sheet  copper  2  mm. 
thick. 

The  further  ends  of  F  and  H  are  connected  with  the  Collie 
apparatus  in  the  manner  shown  in  the  figure.  To  prepare  the 
apparatus  for  use  the  level-bulb  B  is  raised  and  mercury  is 
forced  up  to  the  stopcock  N  and  through  the  stopcock  M  to 
the  end  of  the  branch  tube  C,  and  M  and  N  are  then  closed. 
C  is  now  connected  with  the  gasometer  containing  the  gas 
mixture  to  be  treated,  M  is  opened,  B  is  lowered  and  the  gas 
is  drawn  into  the  bottle  A.  M  is  then  closed.  The  stopcocks 
O  and  P  are  also  closed,  the  tubes  F  and  H  are  heated  and  the 
apparatus  is  exhausted  through  T  by  means  of  a  mercury  pump 
until  gases  cease  to  be  given  off.  T  is  then  closed  and  M  is  care- 
fully turned  to  such  a  position  that  A  communicates  with  D, 
N  is  next  opened  and  then  the  stopcock  P.  Mercury  from  the 
reservoir  K  now  drops  down  through  the  capillary  tube  V  carry- 
ing with  it  gas  into  L  and  forcing  the  gas  through  H.  The  stop- 
cock O  is  turned  so  that  mercury  flows  from  L  into  R  in  a  steady 
stream.  R  is  provided  with  a  side  capillary  tube  W  which  con- 
nects with  the  tube  /,  this  latter  tube  dipping  into  the  mercury 
in  the  reservoir  K.  The  upper  end  of  the  tube  /  is  connected 
through  Z  with  a  water  suction  pump.  A  twisted  piece  of  rusty 
iron  wire  is  inserted  in  the  lower  end  of  the  capillary  tube  W  to 
prevent  the  mercury  that  flows  into  R  from  L  from  completely 
1  Berichte  der  deutschen  chemischen  Gesdlschaft,  43  (1910),  1436. 


212  GAS  ANALYSIS 

closing  the  capillary.  This  results  in  the  mercury  being  drawn 
up  through  W  in  a  series  of  fine  drops  which  fall  into  the  reser- 
voir K.  In  this  manner  the  gases  are  continuously  forced 
through  H  and  A  and  back  through  D,  E  and  F,  and  the  proc- 
ess will  run  for  hours  without  attention  if  the  iron  wire  was 
properly  adjusted  and  the  flow  of  mercury  was  carefully  regu- 
lated at  the  beginning  of  the  experiment. 

Further  amounts  of  the  original  gas  mixture  may  be  intro- 
duced through  C  when  desired.  After  all  of  the  gases  except 
those  of  the  argon  group  have  been  removed,  the  gas  mixture 
remaining  in  the  apparatus  may  be  pumped  out  through  T  by 
means  of  a  Topler  pump,  and  collected  as  described  on  page  13, 
or  the  stopcock  N  may  be  closed,  and  such  of  the  gas  residue 
as  is  in  A  may  be  driven  out  through  C  into  a  suitable  container 
by  raising  the  level-bulb  B  and  turning  the  stopcock  M  into  the 
proper  position. 

For  the  removal  of  large  amounts  of  nitrogen  from  the  air 
Franz  Fischer  and  Ringe  l  have  employed  commercial  calcium 
carbide.  This  substance  reacts  at  high  temperatures  with  ni- 
trogen with  the  formation  of  calcium  cyanamide  and  the  separa- 
tion of  carbon,  according  to  the  equation, 

CaC2  +  N2  =  N  =  C  -  N  =  Ca  +  C. 

They  find  that  this  reaction  does  not  reverse  at  a  temperature  of 
about  800°,  and  that  both  nitrogen  and  oxygen  may  quantita- 
tively be  removed  by  this  means.  The  calcium  carbide  is  placed 
in  a  thick-walled  iron  cylinder  of  sufficient  size  to  hold  about 
seven  kilograms  of  the  carbide.  The  operation  is  conducted  in 
a  manner  essentially  similar  to  that  already  here  described, 
except  that  the  circulating  device  differs  from  that  employed 
by  Collie  and  Travers. 

1  Berichte  der  deutschen  cliemischen  Gesellschaft,  41  (1908),  2017. 


PROPERTIES   OF  THE   VARIOUS   GASES 


213 


GASES  OF  THE  ARGON  GROUP 


ft 

3W 

«      *j  .; 

"rt  tj 

•s-si 

£4 

§ 

ii'l 

|||  ^ 

u  g 

IS 

111 

8:3 

^aa 

<^a^ 

ul 

3 

if 

Helium  . 

1.98 

4-5 

5° 

2.3 

0.000056 

Neon 

9-97 

20 

30 

53° 

29. 

o  .  00086 

Argon     . 

19-95 

83-4 

87 

156° 

52.9 

1  .3 

Krypton      .      . 

4i-5 

104 

121 

211° 

54.3 

0.028 

Xenon    .      .      . 

65-35 

133 

I64 

288° 

57-2 

0.005 

NITROUS  OXIDE 

Properties  of  Nitrous  Oxide.  —  Specific  gravity,  1.5229; 
weight  of  one  liter,  1.9688  grams. 

Nitrous  oxide  is  quite  soluble  in  water.  One  volume  of  water 
dissolves,  at  760  mm.  pressure  and  20°,  0.670  volume  (Carius). 

The  coefficient  of  absorption  is  — 

1.30521  —  o.o45362t  +  0.0006843^. 
For  alcohol  it  is  — 

4.17805  —  0.06981 6  /  +  0.000609  tz, 

and  i  volume  of  alcohol  takes  up  at  20°  3.0253  volumes  N2O. 

Detection  of  Nitrous  Oxide.  —  No  satisfactory  method  has 
yet  been  devised  for  the  detection  of  small  amounts  of  nitrous 
oxide.  Lunge  has  proposed  1  that  the  gas  mixture  under  exami- 
nation be  passed  through  absolute  alcohol  in  which  nitrous 
oxide  is  quite  readily  soluble  while  the  other  gases  with  which 
it  is  usually  associated  are  not  appreciably  dissolved.  The 
method  serves  merely  to  concentrate  the  nitrous  oxide  and 
cannot  be  regarded  as  a  means  of  its  identification. 

1  Berichte  der  deutschen  chemischen  Gesellschaft,  14  (1881),  2188. 


214  GAS  ANALYSIS 

The  procedure  suggested  by  Hempel 1  is  similar  in  character, 
the  gases  being  condensed  by  means  of  liquid  air  and  then  frac- 
tionally distilled.  This  yields  a  residue  rich  in  nitrous  oxide, 
in  which  the  presence  of  the  gas  is  indicated  by  the  increase 
in  volume  that  results  when  it  is  dissociated  by  mixing  with  it 
oxyhydrogen  gas  and  exploding  the  mixture. 

Determination  of  Nitrous  Oxide.  —  For  the  determination 
of  nitrous  oxide  a  variety  of  methods  has  been  proposed.  Wag- 
ner 2  passes  the  gas  over  a  hot  mixture  of  chromium  oxide  and 
sodium  carbonate.  The  nitrous  oxide  is  reduced  to  nitrogen, 
while  any  nitric  oxide  that  may  be  present  is  unaffected.  The 
amount  of  nitrous  oxide  may  be  calculated  from  the  volume  of 
nitrogen  set  free,  or  from  the  amount  of  sodium  chromate  that 
is  formed. 

Von  Dumreicher 3  burns  the  gas  with  hydrogen  in  a  eudiometer. 
Water  and  nitrogen  are  formed,  and  the  latter  is  measured. 
Hempel  recommends  4  this  method  but  adds  oxyhydrogen  gas 
also.  He  uses  his  explosion  pipette  for  the  combustion  and 
finds  that  the  results  are  satisfactory  if  the  volume  of  hydrogen 
is  two  to  three  times  that  of  the  nitrous  oxide  and  if,  further, 
such  an  amount  of  oxyhydrogen  gas  is  added  as  will  give  26  to  64 
volumes  of  combustible  gas  to  every  100  volumes  of  incom- 
bustible gas.  The  decrease  in  volume  is  equal  to  the  volume  of 
nitrous  oxide. 

N2O  +  H2  =  N2  +  H2O 

Von  Knorre  and  Arndt 5  pass  a  mixture  of  nitrous  oxide  and 
hydrogen  through  a  hot  Drehschmidt  capillary  tube  (see  p.  154) 
and  obtain  satisfactory  results.  They  also  find  that  this  method 
gives  approximately  accurate  results  in  the  analysis  of  a  mix- 

1  Zeitschrift  fur  Elektrochcmie,  12  (1906),  600. 

2  Zeitschrift  fiir  analylische  Chemie,  21  (1882),  374. 

3  Kais.  Akad.  d.  Wissen.  Wien.  82  (1881),  560. 

4  Berichte  der  deutschen  ckemischen  Gesellschaft,  15  (1882),  903.    See  also  Ze.il.  jut 
Elccktrochemie,  12  (1906),  600. 

5  Berichte  der  deutschen  chemischen  Gesellschaft,  32  (1899),  2136;  33  (1900),  30. 


PROPERTIES   OF  THE   VARIOUS   GASES  215 

ture  of  nitrous  oxide  and  nitric  oxide.  An  excess  of  hydrogen 
is  added  to  the  gas  mixture  and  the  gases  are  then  slowly  passed 
through  a  Drehschmidt  capillary  tube  heated  to  bright  redness. 

2  NO  +  2  H2  =  N2  +  2  H2O 

Too  rapid  passage  of  the  gas  will  cause  the  formation  of  some 
ammonia  from  the  nitric  oxide. 

2  NO  +  5  H2  =  2  NH3  +  2  H2O 

The  volumes  of  the  two  oxides  of  nitrogen  in  the  gas  mixture 
may  be  calculated  from  the  contraction.  If  V  =  the  volume 
of  the  gas  mixture,  and  C  =  the  contraction,  then 

V  =  vol.  N2O*  +  vol.  NO, 
C  =  vol.  N2O  +  i  J£  vol.  NO, 

and  from  the  foregoing 

vol.  NO  =  2  (C  -  V). 
If  nitrogen  also  is  present,  then 

V  =  vol.  N2O  +  vol.  NO  +  vol.  N2 
C  =  vol.  N2O  +  il/2  vol.  NO 
vol.  H2  =  vol.  N2O  +  vol.  NO, 

from  which  it  follows  that 

vol.  N2O  =  3  vol.  H2  -  2  C 
vol.  NO  =  2  (C  -  vol.  H2) 
vol.  N2  =  V  -  vol.  H2. 

JBaskerville  and  Stevenson  l  determine  nitrous  oxide  by  pass- 
ing the  gas  over  hot  copper,  reducing  the  copper  oxide  by  hydro- 
gen, and  collecting  and  weighing  the  water  that  is  formed.  They 
carry  out  the  method  as  follows:  The  hydrogen  is  generated  in 
a  Kipp  apparatus  from  zinc  and  sulphuric  acid  (i  :6)  to  which 

1  Jour.  Ind.  and  Eng.  Chem.,  3  (1911),  579. 


216  GAS  ANALYSIS 

two  drops  of  chloroplatinic  acid  have  been  added.  The  gas  is 
passed  through  solid  sodium  hydroxide  and  a  long  tube  filled 
with  calcium  chloride  to  remove  acid  gases  and  moisture.  The 
calcium  chloride  tube  is  connected  to  a  combustion  tube  of  hard 
glass  that  is  100  cm.  long  and  is  filled  for  70  cm.  of  its  length 
with  snugly  fitting  rolls  of  copper  gauze.  The  further  end  of  the 
combustion  tube  is  drawn  out  to  fairly  small  diameter,  and  the 
end  is  inserted  into  a  tube  filled  with  calcium  chloride,  the  joint 
between  the  two  being  made  air  tight  with  a  piece  of  rubber 
tubing.  A  second  tube  filled  with  calcium  chloride  is  joined  to 
the  first  and  to  the  further  end  of  this  tube  there  is  connected  a 
delivery  tube  that  dips  into  water  or  some  other  liquid  in  a  test 
tube  and  serves  to  show  the  speed  of  flow  of  the  gas.  The  com- 
bustion tube  rests  upon  an  iron  trough  in  a  combustion  furnace. 
Hydrogen  is  now  passed  through  the  combustion  tube  until 
most  of  the  air  has  been  expelled.  The  tube  is  then  heated  to 
dull  redness  and  the  passage  of  hydrogen  is  continued  until  the 
copper  is  completely  reduced.  The  tubes  containing  calcium 
chloride  are  weighed  and  are  now  connected  to  the  combustion 
tube  in  the  manner  above  described.  The  hydrogen  is  then  dis- 
continued and  about  800  cc.  of  the  gas  sample  is  passed  into  the 
tube  that  contains  sodium  hydroxide  and  through  the  rest  of  the 
apparatus,  the  speed  of  flow  of  the  gas  being  about  two  bubbles 
per  second.  The  volume  of  the  gas  sample  and  its  temperature 
and  pressure  are  noted  before  the  gas  is  passed  through  the  ap- 
paratus. To  insure  complete  decomposition  of  the  nitrous 
oxide  by  the  hot  copper  the  operation  should  be  so  conducted 
that  the  last  15  cm.  of  copper  gauze  undergoes  no  oxidation. 
After  the  sample  of  gas  has  been  passed  through  the  chain, 
hydrogen  is  again  admitted  to  the  apparatus  and  is  passed 
through  it  at  the  rate  of  from  three  to  four  bubbles  per  second 
until  the  copper  oxide  that  has  been  formed  is  entirely  reduced, 
and  the  water  is  completely  driven  out  of  the  tube  and  into  the 
weighed  tubes  containing  calcium  chloride.  The  operation  is 
then  presumably  completed,  although  the  authors  give  no 


PROPERTIES   OF  THE   VARIOUS   GASES  217 

further  details,  by  discontinuing  the  heating  of  the  combustion 
tube  and,  when  the  apparatus  is  cold,  passing  dry  air  through 
the  calcium  chloride  tubes  until  the  hydrogen  with  which  they 
are  filled  is  displaced.  They  are  then  weighed  and  the  amount 
of  nitrous  oxide  in  the  gas  sample  is  calculated  from  the  weight 
of  water  that  has  been  formed. 

The  method  cannot  be  used  for  the  determination  of  nitrous 
oxide  in  gas  mixtures  that  contain  other  oxides  of  nitrogen  or 
oxygen  or  other  gases  that  would  be  decomposed  by  the  metallic 
copper  with  the  formation  of  copper  oxide,  unless  the  amounts  of 
these  gases  are  determined  and  the  water  that  results  from  them 
is  subtracted  from  the  total  amount  of  water  found.  Baskerville 
and  Stevenson  find  that  these  gases  are  not  present  in  the 
samples  of  commercial  compressed  nitrous  oxide  that  they 
analyzed. 

NITRIC  OXIDE  (NO) 

Properties  of  Nitric  Oxide.  —  Specific  gravity,  1.0378; 
weight  of  one  liter,  1.3417  grams. 

Nitric  oxide  is  but  slightly  soluble  in  water,  one  volume  of 
water  dissolving  only  about  ^  volume  of  the  gas.  It  is  more 
soluble  in  alcohol,  the  coefficient  of  absorption  for  temperatures 
between  o°  and  25°  being,  according  to  Carius, 

0.31606  —  0.003487  t  +  0.000049  t2* 

Nitric  oxide  cannot  be  kept  over  water  without  undergoing 
change.  Nitrous  acid  is  formed  together  with  some  hyponitrous 
acid  which  breaks  down  partly  into  nitrous  oxide  and  partly 
into  ammonia.  The  latter  then  reacts  with  the  nitrous  acid  and 
liberates  nitrogen,  which  accounts  for  the  presence  of  this  gas  in 
quite  large  amount  in  nitric  oxide  that  has  been  stored  over 
water  for  a  considerable  length  of  time. 

Nitric  oxide  is  absorbed  by  solutions  of  ferrous  salts,  potassium 
permanganate,  potassium  dichromate,  and  alkaline  sodium 
sulphite.  It  is  also  taken  up  by  concentrated  sulphuric  acid, 


218  GAS  ANALYSIS 

one  cc.  of  this  acid  of  1.84  specific  gravity  absorbing  0.035  cc-  of 
nitric  oxide.  If  the  acid  has  a  specific  gravity  of  1.5,  one  cc.  of  it 
will  absorb  0.017  cc*  °f  the  gas. 

Hydrogen  dioxide  reacts  with  nitric  oxide  to  form  nitric  acid 
and  water. 

Detection  of  Nitric  Oxide.  —  A  delicate  method  for  the  de- 
tection of  nitric  oxide  consists  in  passing  the  gas,  mixed  with  air, 
through  a  dilute  solution  of  the  hydroxide  of  either  sodium  or 
potassium  and  adding  Griess's  reagent.  The  reactions  that  take 
place  in  the  absorption  are,  according  to  Le  Blanc,1  as  follows: 

2  NO  +  O2  — >>  2  NO2, 

NO  +  NO2  —  -»  N2O3, 

NO2  +  absorbent  — >  nitrate  and  nitrite, 

N20s  +  absorbent  — >  nitrite. 

The  nitrite  that  has  thus  been  formed  in  the  absorbent  is 
detected  by  first  adding  acetic  acid  to  the  sodium  hydroxide  or 
potassium  hydroxide  until  the  solution  has  a  faint  acid  reaction 
and  then  adding  Griess's  reagent  as  improved  by  Ilosvay  2  and 
Lunge.3  The  reagent  in  this  modified  form  is  prepared  as 
follows:  0.5  gram  of  sulphanilic  acid  is  dissolved  in  150  cc.  of 
dilute  acetic  acid,  o.i  gram  of  solid  a-naphthylamine  is  boiled 
with  20  cc.  of  water,  the  colorless  solution  is  poured  off  from  the 
violet  residue  and  to  the  solution  150  cc.  of  dilute  acetic  acid  is 
added.  The  two  solutions  are  then  mixed  and  the  reagent  is 
kept  in  a  tightly  stoppered  bottle. 

Lunge  states  that  the  reagent  is  not  at  all  affected  by  the 
light.  This  is  contradicted  by  Reckleben,  Lockemann  and 
Eckardt  4  who  state  that  even  in  diffused  daylight  the  reagent 
soon  takes  on  a  yellowish-red  color  which  renders  the  detection 
of  small  amounts  of  nitrous  acid  impossible.  They  find  that  if 

1  Zeit.  fur  Elektrochemie,  12  (1906),  541. 
*Bull.  soc.  chim.  (3),  2  (1889),  347. 

3  Z.f.  angew.  Chem.,  1889,  666. 

4  Z.f.  analyt.  Chem.,  46  (1907),  671. 


PROPERTIES  OF  THE  VARIOUS  GASES  219 

the  solution  is  kept  in  the  dark  it  remains  completely  clear  and 
colorless  for  months. 

In  making  the  test  the  acidified  solution  of  the  absorbent  is 
warmed  to  about  80°  and  about  one-fifth  of  its  volume  of  the 
Griess's  reagent  is  added.  If  nitric  oxide  was  present  in  the  gas 
mixture,  the  solution  turns  red.  The  reaction  is  extremely 
delicate,  one  part  of  nitrous  acid  in  one  thousand  million  parts 
of  the  solution  giving  a  distinct  red  coloration  after  one  minute. 

Determination  of  Nitric  Oxide.  —  Nitric  oxide  may  quanti- 
tatively be  determined  by  absorption  of  the  gas  with  a  solution 
of  ferrous  sulphate.  The  reagent  contains  one  part  by  weight 
of  the  salt  dissolved  in  two  parts  by  weight  of  water,  and  it  is 
very  slightly  acidified  with  dilute  sulphuric  acid.  It  is  used  in 
a  Hempel  double  pipette  for  liquid  reagents.  The  analytical 
absorbing  power  of  this  solution  15-2.5.  This  reagent,  however, 
tends  to  give  up  the  absorbed  nitric  oxide  to  indifferent  gases, 
and  the  method  does  not  yield  correct  results  when  nitrous  oxide 
is  present  with  the  nitric  oxide. 

It  has  been  proposed  to  determine  nitric  oxide  by  mixing  it 
with  hydrogen  and  burning  the  mixture  in  a  Drehschmidt  cap- 
illary tube  (see  under  Nitrous  Oxide) .  Moser,  who  has  recently 
made  a  careful  comparison  of  the  various  methods  for  the  deter- 
mination of  this  gas  states 1  that  this  method  does  not  yield  uni- 
form results  both  because  of  the  secondary  reaction  which  causes 
the  formation  of  ammonia  and  because  of  the  porosity  of  red- 
hot  platinum  to  gases. 

The  absorption  of  nitric  oxide  by  sodium  sulphite  is  original 
with  Divers,2  who,  however,  gives  no  details  concerning  the 
preparation  of  this  solution  further  than  to  say  that  it  is  "a 
strong  solution  of  either  sodium  or  potassium  sulphite  to  which 
a  little  alkali  hydroxide  has  been  added."  He  states  that  it 
"  quickly  absorbs  every  trace  of  nitric  oxide,  which  it  fixes  in 
the  form  of  hyponitrososulphate,  Na2N202SOa." 

1  Z.f.  analyt.  Chem.,  50  (1911),  401. 
*Jour.  Chem.  Soc.,  75  (1899),  82. 


220  GAS  ANALYSIS 

Moser  finds  that  this  reagent  is  not  superior  to  ferrous  sul- 
phate and  that  the  absorption  by  sodium  sulphite  takes  place 
quite  slowly  and  is  complete  only  after  long  shaking. 

A  satisfactory  titrimetric  method  for  the  determination  of 
nitric  oxide  is  that  based  upon  the  reaction  between  the  gas 
and  an  acidulated  solution  of  potassium  permanganate. 

10  NO  +  6  KMnO4  +  9  H2SO4  = 

3  K2SO4  +  6  MnSO4  +  10  HNO3  +  4  H2O. 

The  reaction  was  first  examined  by  Terreil 1  who  found  that 
nitric  oxide  is  completely  oxidized  to  nitric  acid  by  a  neutral 
or  an  acidified  solution  of  potassium  permanganate,  while 
nitrous  oxide  is  not  attacked.  Lunge  2  ascertained  that  the 

speed  of  reaction  between  nitric  oxide  and  a  y~  solution  of  po- 
tassium permanganate  is  so  slight  that  complete  absorption 
of  the  gas  is  attained  only  when  an  apparatus  that  brings  about 
prolonged  and  intimate  contact  between  the  gas  and  absorbent 
is  employed.  He  recommends  for  this  purpose  the  ten-bulb 
tube  shown  on  page  359,  but  better  results  will  undoubtedly 
follow  the  employment  of  a  Friedrichs  spiral  gas  washing  bottle, 
page  123.  Before  beginning  the  determination  the  air  in  the 
apparatus  must  be  displaced  by  carbon  dioxide  because  of  the 
reaction  between  nitric  oxide  and  oxygen.  To  avoid  this  opera- 
tion and  also  to  obtain  more  complete  absorption,  Moser 3 
suggests  that  the  gas  mixture  be  passed  into  a  spiral  absorption 
bulb  that  is  made  entirely  of  glass  and  that  is  figured  in  his  arti- 
cle. A  simple  and  satisfactory  substitute  for  this  spiral  bulb 
may  be  made  by  fusing  to  one  of  the  tubes  of  the  bulb  of  a  Hem- 
pel  gas  pipette  of  about  130  cc.  capacity  a  capillary  tube  about 
3.5  cm.  long,  and  to  the  other  tube  of  the  bulb  a  piece  of  glass 
tubing  about  i  cm.  external  diameter  and  20  cm.  long.  The  bulb 
is  placed  in  a  clamp  with  the  short  capillary  tube  uppermost, 

1  Complex  rendus,  63  ( 1 866) ,  970. 

2  Z.f.  angew.  Chem.,  1890,  567. 

3  Loc.  cit. 


PROPERTIES   OF  THE   VARIOUS   GASES  221 

and  the  long  stem  is  inserted  into  a  wide  mouth  bottle  of  about 
250  cc.  capacity  in  which  is  placed  a  measured  volume  (about 
200  cc.)  of  the  standardized  solution  of  potassium  permanganate. 
The  potassium  permanganate  is  approximately '  decinormal  in 
strength  and  to  every  100  cc.  of  the  solution  is  added  from  30  to 
50  cc.  of  2  N  sulphuric  acid.  The  capillary  tube  of  the  bulb  is 
closed  by  a  short  piece  of  rubber  tubing  and  pinchcock.  A  water 
suction  pump  is  connected  to  this  tube,  and  the  permanganate 
solution  is  drawn  up  until  it  fills  the  tube  and  reaches  nearly  to 
the  top  of  the  capillary  tube.  The  gas  burette  containing  the 
sample  of  gas  under  examination  is  connected  with  the  bulb 
by  means  of  the  usual  piece  of  bent  capillary  tubing  and  the 
gas  sample  is  passed  over  into  the  bulb.  The  pinchcock  at  the 
top  of  the  bulb  is  then  closed  and  the  bulb  is  disconnected  from 
the  burette.  The  bottle  is  grasped  in  the  left  hand  and  the  lower 
tube  of  the  bulb  in  the  right  hand,  and  with  the  end  of  the  large 
tube  of  the  bulb  resting  upon  the  bottom  of  the  bottle,  the  bulb 
is  shaken  for  about  ten  minutes  to  effect  complete  reaction  .be- 
tween the  nitric  oxide  and  the  potassium  permanganate.  The 
pinchcock  at  the  top  of  the  bulb  is  then  opened  and  the  solu- 
tion is  allowed  to  run  out  of  the  bulb  down  into  the  bottle,  the 
bulb  being  finally  rinsed  with  distilled  water.  An  excess  of  a 
standardized  solution  of  ferrous  sulphate  is  added  to  the  po- 
tassium permanganate  and  the  excess  of  ferrous  sulphate  is 
titrated  back  with  potassium  permanganate. 

The  results  by  this  method  even  when  the  Moser  absorption 
bulb  is  employed  are  somewhat  lower  than  those  obtained  by 
absorption  with  ferrous  sulphate,  which  Moser  ascribes  to  the 
reaction  between  the  nitric  oxide  and  the  oxygen  dissolved  in 
the  solution  of  potassium  permanganate. 

Schonbein  l  found  that  when  nitric  oxide  was  brought  into 
contact  with  an  excess  of  hydrogen  dioxide  the  gas  is  oxidized  to 
nitric  acid: 

2  NO  +  3  H2O2  =  2  HN03  +  2  H2O 

1 /./.  prakt.  Chem.,  81  (1860),  265. 


222  GAS  ANALYSIS 

The  applicability  of  this  reaction  to  the  determination  of 
nitric  oxide  has  been  studied  by  Davis,1  by  Wilfarth  2  and  by 
Lunge.3  Lunge  discarded  the  method  because  his  experiments 
indicated  that  the  absorption  of  nitric  oxide  by  hydrogen  dioxide 
either  in  acid  or  in  alkaline  solution  was  not  complete.  Moser  4 
found  that  this  criticism  is  correct  when  the  method  is  carried 
out  in  the  manner  described  by  Wilfarth  and  by  Lunge,  but 
he  states  that  with  the  absorption  bulb  that  he  devised  it  is 
possible  to  obtain  complete  oxidation  of  nitric  oxide  in  from  six 
to  twelve  minutes.  He  employs  as  absorbent  a  three  per  cent 
solution  of  hydrogen  dioxide  in  a  definite  volume  of  which  (about 
no  cc.)  the  free  acid  is  first  determined  by  titration  with  a  stan- 
dardized solution  of  potassium  hydroxide,  using  a  one  per  cent 
solution  of  phenolphthalein  as  indicator.  The  reagent  is  then 
brought  into  the  absorption  bulb,  the  gas  is  passed  in  from  a 
gas  burette,  and  the  gas  and  hydrogen  dioxide  are  shaken  to- 
gether for  several  minutes.  The  absorbent  is  then  transferred 
to  a  beaker  and  the  nitric  acid  that  has  been  formed  is  titrated 
with  potassium  hydroxide.  If  acid  or  alkaline  gases  are  present 
in  the  gas  mixture  under  examination  they  must  first  be  re- 
moved by  passing  the  mixture  through  suitable  absorption  ap- 
paratus. Under  such  conditions,  however,  the  determination  of 
the  nitric  oxide  with  potassium  permanganate  is  preferable  to 
that  with  hydrogen  dioxide. 

Determination  of  Nitrites  in  the  Atmosphere. — The  method 
of  Ilosvay  and  Lunge  for  the  detection  of  nitrites  may  also  be 
employed  for  the  determination  of  nitrites  in  the  atmosphere. 
A  measured  amount  of  air  is  drawn  through  a  solution  of  sodium 
hydroxide  or  potassium  hydroxide  and  the  color  that  results 
when  Griess's  reagent  is  added  under  the  conditions  above  pre- 
scribed is  compared  with  the  color  yielded  by  a  standard  ni- 
trite solution.  For  approximate  work  the  standard  solution 

1  Chemical  News,  41  (1880),  188. 
2Z.f.  analyt.  Chem.,  23  (1884),  587. 

3  Z.f:  angew.  Chem.,  1890,  568. 

4  Loc.  cit. 


PROPERTIES  OF  THE  VARIOUS   GASES  223 

may  be  prepared  by  dissolving  a  weighed  amount  of  either 
potassium  nitrite  or  sodium  nitrite  in  water.  If  greater  accuracy 
is  desired  the  standard  nitrite  solution  may  be  prepared  by  pre- 
cipitating a  solution  of  silver  nitrate  with  sodium  nitrite,  re- 
crystallizing  the  silver  nitrite  twice  from  hot  water  and  then 
adding  to  its  solution  in  hot  water  sodium  chloride,  and  remov- 
ing the  precipitated  silver  chloride  by  filtration. 

NITROGEN  TETROXIDE 

Properties  of  Nitrogen  Tetroxide. —  Specific  gravity  (NO2), 
1.5906.  Weight  of  one  liter  (NO2),  2.0563  grams.  The  mole- 
cule of  nitrogen  tetroxide  is  considered  to  have  the  formula  N2O4 
at  temperatures  below  —  11°  and  to  dissociate  into  NO2  as  the 
temperature  rises.  At  the  average  temperature  of  the  laboratory 
the  gas  will  contain  both  the  simpler  molecule  NC>2  and  the 
polymer  ^64. 

When  brought  into  contact  with  water,  nitrogen  tetroxide 
forms  nitric  acid,  nitrous  acid  and  nitric  oxide,  according  to 
the  equations 

ON-ON02  +  H20  =  HONO2  +  HO-NO, 
3  ON-ONO2  +  2  H20  =  4  HONO2  +  2  NO. 

When  nitrogen  tetroxide  is  passed  through  a  dilute  solution  of 
sodium  hydroxide,  oxygen  or  air  being  absent,  sodium  nitrite 
and  nitrate  are  formed  l  in  the  proportions  shown  in  the  first 
equation  above.  If,  however,  oxygen  or  atmospheric  air  is 
present  with  the  nitrogen  tetroxide,  some  of  the  nitrite  is  oxidized 
to  nitrate.  The  gas  is  rapidly  absorbed  by  concentrated  sul- 
phuric acid  (1.7  to  1.8  sp.  gr."),  nitrosyl  sulphuric  acid  and  nitric 
acid  being  formed. 

ON-0-NO2  +  S02  (OH)2  =  S02  (OH)  (ONO)  +  HO-NO2 

1  Lunge  and  Berl,  Z.f.  angewandte  Chem.,  19  (1906),  857. 


224  GAS  ANALYSIS 

Nitrogen  tetroxide  may  be  detected  by  absorbing  the  gas 
in  a  dilute  solution  of  sodium  hydroxide,  acidifying  this  with 
acetic  acid  and  adding  Griess's  reagent.  (See  under  Nitric 
Oxide.) 

AMMONIA    (NH3) 

Properties  of  Ammonia.  —  Specific  gravity,  0.5895;  weight 
of  one  liter,  0.7621  gram.  One  gram  of  water  absorbs,  at  a 
pressure  of  760  mm., 

at    o°,  0.875  gram    (1129  cc.) 
"  10°,  0.679     "       (  876  "  ) 

"    20°,  0.526        *          (    678    "    ) 

Alcohol  and  ether  also  absorb  considerable  quantities  of  the 
gas. 

Detection  of  Ammonia.  —  Ammonia  may  be  detected  when 
present  in  fairly  large  amounts  by  means  of  litmus  paper  or 
turmeric  paper.  A  more  sensitive  reagent  for  the  detection  of 
minute  amounts  of  ammonia  is  Nessler's  reagent  which  is  an 
alkaline  solution  of  potassium  mercuric  iodide,  K^Hgl^  When 
ammonia  acts  upon  this  solution  mercurammonium  iodide 


N=Hg 
M 

is  formed.  If  the  amount  of  ammonia  is  appreciable,  the  com- 
pound appears  as  a  reddish  brown  precipitate.  With  smaller 
amounts  of  ammonia  it  imparts  merely  a  yellow  color  to  the 
solution.  The  reaction  is  very  delicate;  0.05  mg.  of  ammonia  in 
one  liter  of  water  can  readily  be  detected. 

Determination  of  Ammonia.  —  Ammonia  may  be  determined 
by  passing  the  gas  mixture  through  a  measured  amount  of  dilute 
hydrochloric  or  sulphuric  acid  of  known  strength  and  titrating 
the  excess  of  acid  with  a  standard  solution  of  an  alkali,  using 
litmus  or  methyl  orange  as  indicator. 


PROPERTIES  OF  THE  VARIOUS   GASES  225 

If  the  amount  of  ammonia  in  the  gas  mixture  is  very  small,  as 
for  example  in  atmospheric  air,  the  ammonia  may  be  absorbed 
by  passing  it  through  ammonia-free  distilled  water  slightly 
acidified  with  sulphuric  acid  and  then  determining  the  ammonia 
colorimetrically  with  Nessler's  reagent. 

CARBON   DIOXIDE    (C02) 

Properties  of  Carbon  Dioxide.  —  Specific  gravity,  1.5201; 
weight  of  one  liter,  1.9652  grams. 

According  to  Naccari  and  Pagliani  one  volume  of  water  ab- 
sorbs, between  17°  and  27°, 

1.5062  —  0.036511  /  -+-  0.0002917  /2. 

One  cc.  of  sulphuric  acid  (sp.  gr.  =  1.78)  dissolves,  at  14°  C. 
and  816.4  mm-  pressure,  1.16  cc.  of  carbon  dioxide. 

Carbon  dioxide  is  readily  absorbed  by  a  solution  of  potassium 
hydroxide  or  of  barium  hydroxide. 

Determination  of  Carbon  Dioxide. —  For  the  volumetric  de- 
termination of  the  gas,  a  solution  of  one  part  of  caustic  potash 
in  two  parts  of  water  is  employed.  The  analytical  absorbing 
power  of  this  solution  is  40.  For  the  rapid  and  approximate 
determination  of  carbon  dioxide  by  means  of  this  absorbent, 
the  Honigmann  gas  burette  (page  7  2)  may  be  used.  With  the 
Bunte  gas  burette  (page  74)  somewhat  -  more  accurate  results 
can  be  obtained. 

The  most  satisfactory  forms  of  absorbing  apparatus  for  use  in 
technical  gas  analysis  are  the  spiral  pipette  described  on  p.  81 
or  the  Hempel  simple  pipette  for  solid  and  liquid  reagents 
(Fig.  35).  With  the  latter  the  cylindrical  part  C  is  first  closely 
filled  with  very  short  rolls  of  iron  wire  gauze.  The  gauze  has 
a  mesh  of  i  to  2  mm.,  and  the  rolls  are  from  i  to  2  cm.  long  and 
about  5  mm.  thick.  The  high  viscosity  of  the  reagent  causes 
it  to  cling  to  the  wire  gauze  when  the  gas  is  passed  into  the  pi- 
pette and,  as  a  consequence,  the  absorption  of  the  carbon 


226  GAS  ANALYSIS 

dioxide  is  very  rapid.  The  viscosity  of  the  reagent  serves  also 
to  protect  the  iron  wire  gauze  from  oxidation  by  any  oxygen 
in  the  gas  mixture.  Unless  the  amount  of  carbon  dioxide  in  a 
gas  mixture  is  unusually  high,  it  is  quantitatively  removed  by 
simply  passing  the  gas  once  into  either  pipette  and  allowing  it 
to  remain  there  a  few  seconds. 

Special  methods  for  the  determination  of  small  percentages 
of  carbon  dioxide  such  as  are  found,  for  example,  in  atmospheric 
air  are  described  in  Chapter  XVIII. 

CARBON   MONOXIDE    (CO) 

Properties  of  Carbon  Monoxide.  —  Specific  gravity,  0.9673 ; 
weight  of  one  liter,  1.2506  grams.  One  volume  of  water  dis- 
solves, according  to  L.  W.  Winkler, 

at    o°,  0.03537  vo1-  of  CO 
"  10°,  0.02816 

"    20°,  0.02319  " 

According  to  Carius,  alcohol  dissolves,  between  o°  and  25°, 
0.20443  volume  of  carbon  monoxide. 

Detection  of  Carbon  Monoxide  by  Blood  Spectrum. — The 
most  delicate  and  dependable  method  for  the  detection  of  carbon 
monoxide  is  that  in  which  the  gas  is  absorbed  by  a  solution  of 
blood  and  the  resulting  carbon  monoxide  haemoglobin  is  de- 
tected by  the  spectroscope.  When  a  dilute  solution  of  pure 
blood  is  brought  before  the  slit  of  the  spectroscope,  two  absorp- 
tion bands,  lying  between  the  Fraunhofer  lines  D  and  E,  are 
seen  (Fig.  83,  spectra  No.  i  and  No.  2).  If,  now,  a  reducing 
agent,  such  as  ammonium  sulphide,  is  added  to  the  blood  solu- 
tion, these  two  bands,  which  are  due  to  the  oxyhaemoglobin  of 
the  blood,  disappear  and  are  replaced  by  a  single  broad  and 
weakly  denned  band  (spectrum  No.  4). 

When,  however,  carbon  monoxide  has  previously  been 
brought  into  contact  with  the  blood  solution,  the  two  absorption 


PROPERTIES   OF  THE  VARIOUS   GASES 


227 


bands  due  to  carbon  monoxide  haemoglobin  (spectrum  No.  3) 
do  not  disappear  when  the  reducing  agent  is  added.  Conse- 
quently the  persistence  of  these  two  separate  absorption  bands 
is  conclusive  proof  of  the  presence  of  carbon  monoxide  in  the 
gas  mixture  under  examination. 

The  solution  of  blood  for  use  in  this  test  is  prepared  by  freeing 
a  sample  of  blood  from  fibrin  by  beating  it  with  a  bundle  of 
straws  and  then  diluting  the  clear  blood  with  an  equal  volume 
of  a  cold,  saturated  solution  of  borax.  The  addition  of  borax 

BC      D          Eb        F  G 

Pure  blood  highly  diluted 


Blood  highly  diluted  +  CO 

Blood  highly  diluted 

+  NH4SH 


FIG.  83 


prevents  putrefaction  and  does  not  change  the  spectroscopic 
properties  of  the  blood,  reduction  and  combination  with  oxygen 
and  carbon  monoxide  taking  place  just  as  readily  as  if  fresh 
blood  or  a  solution  of  haemoglobin  were  employed.  The  solu- 
tion used  in  the  absorption  of  carbon  monoxide  is  prepared  from 
the  concentrated  solution  by  mixing  one  cc.  of  the  latter  with 
19  cc.  of  water.  This  gives  a  blood  solution  of  the  concentration 
i  in  40.  The  absorption  of  carbon  monoxide  by  this  dilute 
blood  solution  may  be  effected  by  filling  a  100  cc.  bottle  with 
water,  emptying  it  in  the  room  of  which  the  air  is  to  be  tested 
for  carbon  monoxide,  introducing  3  cc.  of  the  dilute  blood 
solution  into  the  bottle,  inserting  the  stopper  in  the  bottle  and 
then  thoroughly  shaking  the  bottle  to  bring  the  blood  into  con- 
tact with  the  inclosed  gas.  A  more  efficient  absorption  appa- 
ratus is  that  designed  by  Wolff1  (Fig.  84).  In  preparing  this 

1  Correspondenzblatt  des  Vereins  analytischer  Chemiker,  3  (1880),  46. 


228 


GAS   ANALYSIS 


apparatus  for  use  a  small  wad  of  glass  wool  is  inserted  into  d 
from  above  and  gently  pressed  into  place.  The  tube  is  then 
filled  up  to  /  with  moderately  fine,  powdered  glass.  The  grains 
of  glass  should  be  about  as  large  as  those  of  ordinary  gunpowder 
and  before  its  introduction  into  the  tube  the  glass  should  be 
thoroughly  cleaned  by  boiling  it  with  hydrochloric  acid,  and 
washing  it  with  distilled  water.  Two  cc.  of  the  dilute  blood 
solution  (i  in  40)  is  then  introduced  through  a  from  a  pipette. 

a  is  closed  and  by  gen- 
tly blowing  into  h  the 
blood  solution  is  caused 
to  uniformly  distribute 
itself  throughout  the 
column  of  powdered 
glass.  The  side  tube  e 
is  now  connected  with 
the  gas  mixture  (air) 


that  is  to  be  tested  for 
carbon  monoxide,  and 
the  gas  is  driven  or 
drawn  through  the  ab- 
sorption tube,  its  vol- 
ume being  measured 
by  a  gas  meter  or 
other  suitable  device 
attached  to  h.  To  pre- 
vent the  evaporation  of 

the  water  from  the  blood  solution  in  the  absorption  apparatus, 
it  is  advisable  to  insert  between  e  and  the  source  of  gas  a 
U-tube  or  wash  bottle  containing  sufficient  water  to  keep  the 
entering  air  saturated  with  moisture.  If  only  very  small 
amounts  of  carbon  monoxide  are  to  be  expected,  a  sample  of  air 
of  about  10  liters  should  be  passed  through  the  absorption  appa- 
ratus at  a  rate  of  about  3  liters  per  hour.  If  it  is  not  convenient 
to  set  up  the  apparatus  in  or  near  the  room  whose  atmosphere 


FIG.  84 


PROPERTIES  OF  THE   VARIOUS   GASES  229 

is  to  be  tested,  the  sample  may  be  collected  in  a  10  liter  bottle 
by  filling  the  bottle  with  water  and  emptying  it  in  the  room. 

After  the  absorption  of  carbon  monoxide  by  the  blood  solu- 
tion has  been  accomplished  in  either  of  the  two  ways  above 
described,  it  is  transferred  to  a  small  test  tube  and  examined 
with  a  spectroscope.  If  the  Wolff  absorption  tube  has  been 
used,  the  blood  solution  is  removed  after  the  test  by  taking 
out  the  stoppers  a  and  c,  placing  the  test  tube  under  c,  and 
slowly  dropping  pure  water  upon  the  powdered  glass.  The 
liquid  is  collected  in  the  test  tube  until  the  volume  amounts 
to  3  cc.  Since  2  cc.  of  the  dilute  blood  solution  (i  in  40)  was 
originally  used,  the  resulting  3  cc.  of  solution  would  now  have 
a  concentration  of  i  in  60. 

Any  spectroscope  of  not  too  great  dispersion  may  of  course  be 
employed  for  the  examination  of  the  blood  spectrum,  but  a 
small  direct  vision  spectroscope  is  quite  as  satisfactory  for  this 
purpose  as  a  larger  one.  For  checking  the  result  of  the  spec- 
troscopic  examination  a  second  small  test  tube  should  be  filled 
with  the  original  blood  solution,  also  diluted  to  i  in  60,  that  has 
not  been  exposed  to  the  action  of  the  gas.  One  drop  of  a  strong 
solution  of  ammonium  sulphide  is  added  to  the  contents  of 
each  tube,  the  tubes  are  corked  and  thoroughly  shaken,  and 
the  spectra  are  examined  after  the  tubes  have  stood  for  about 
half  an  hour.  The  presence  of  the  two  absorption  bands 
shown  in  Fig.  83,  spectrum  No.  3,  in  the  J)lood  solution  that  has 
been  exposed  to  the  gas,  and  the  absence  of  these  bands  in  the 
solution  of  pure  blood  is  conclusive  proof  of-  the. presence  of 
carbon  monoxide  in  the  air  under  examination.  When  the  test 
is  made  in  this  manner  the  delicacy  of  the  method  is  about  0.03 
per  cent  by  volume  of  carbon  monoxide. 

Kostin  has  found  l  that  if  the  oxygen  of  the  air  is  first  removed, 
the  delicacy  of  the  blood  test  for  carbon  monoxide  is  greatly 
enhanced,  and  that  under  these  conditions  one  part  of  the  gas  in 
forty  thousand  parts  of  air  may  be  detected.  The  removal  of 

1  Archivfur  die  Gesammte  Physiologic,  83  (1901),  572. 


230 


GAS  ANALYSIS 


oxygen  may  be  effected  by  passing  the  air  through  3  liters  of  a 
saturated  solution  of  ferrous  sulphate  to  which  i  liter  of  strong 
ammonium  hydroxide  has  been  added.  The  solution  is  placed 
in  an  aspirator  bottle  that  is  filled  with  iron  wire  gauze  (A, 
Fig.  85).  Four  liters  of  this  solution  which  contains  much 
undissolved  ferrous  hydroxide  is  able  to  absorb  the  oxygen 
contained  in  80  liters  of  air.  Two  such  bottles  are  employed, 
the  air  under  examination  being  first  drawn  into  one  and  then 


FIG.  85 

driven  into  over  the  other,  and  passed  backwards  and  forwards 
between  the  two  aspirators  until  all  oxygen  has  been  removed. 
The  residual  gas  is  next  forced  from  one  aspirator  into  the  other 
through  one  of  the  washing  flasks  BB'  and  the  absorption  ap- 
paratus K  containing  the  blood  solution.  The  washing  flasks 
are  charged  with  oxalic  acid  for  the  removal  of  any  ammonia 
that  may  be  given  off  from  the  material  in  the  aspirator  bottles. 
Ogier  and  Kohn-Abrest  remove  1  oxygen  by  means  of  a  solu- 

1  Ann.  chim.  analyt.  appl.,  13  (1908),  218. 


PROPERTIES  OF  THE  VARIOUS   GASES  231 

tion  of  sodium  hyposulphite,  which  is  probably  more  rapid  in 
its  action  and  more  convenient  to  handle  than  is  the  reagent 
used  by  Kostin. 

Some  investigators  are  of  the  opinion  that  the  best  method 
for  detecting  the  presence  of  carbon  monoxide  in  blood  is  that 
suggested  by  Kunkel.  The  blood  is  here  diluted  with  10  volumes 
of  water  and  an  equal  volume  of  a  3  per  cent  tannin  solution  is 
then  added.  If  the  blood  contains  carbon  monoxide,  a  reddish 
precipitate  is  formed,  while  with  normal  blood  the  precipitate 
is  dark  brown.  These  color  reactions  become  especially  distinct 
after  five  or  six  hours. 

On  the  other  hand,  Doepner  1  states  that  the  spectroscopic 
detection  of  carbon  monoxide  in  blood  is  fully  as  satisfactory  as 
the  best  of  the  precipitation  methods. 

Detection  of  Carbon  Monoxide  by  means  of  Iodine  Pent- 
oxide. —  Iodine  pentoxide  and  carbon  monoxide  react  on  each 
other  with  the  liberation  of  free  iodine  and  the  formation  of 
carbon  dioxide. 

I2O5  +  5  CO  =  2  I  +  5  CO2 

C.  de  la  Harpe  and  Reverdine  2  first  utilized  this  reaction  for  the 
detection  of  carbon  monoxide.  More  recently  Levy  and  Pecoul 3 
find  that  by  passing  the  liberated  iodine  into  chloroform,  minute 
amounts  of  carbon  monoxide  in  air  can  be  detected.  They  state 
that  one  volume  of  carbon  monoxide  in  10,000  volumes  of  air 
will  set  free  sufficient  iodine  to  give  to  the  chloroform  an  intense 
color.  If  acetylene  is  present  in  no  greater  proportion  than 
i :  10,000,  it  will  cause  no  coloration  of  the  chloroform,  but  larger 
amounts  of  acetylene  should  be  removed  before  the  test  is  made. 

Determination  of  Carbon  Monoxide  by  Absorption.  —  For 
the  absorption  and  volumetric  determination  of  carbon  monox- 
ide a  hydrochloric  acid  or  an  ammoniacal  solution  of  cuprous 
chloride  is  employed. 

1  Z.  /.  Medizinalbeamte,  22  (1909),  287. 

2  Ghent.  Ztg.  12  (1888),  1726. 

3  Comptes  rendus,  142  (1906),  162. 


232  GAS  ANALYSIS 

The  hydrochloric  acid  solution  of  cuprous  chloride  may  be 
prepared,  according  to  Winkler,  by  adding  a  mixture  of  86 
grams  of  copper  oxide  and  17  grams  of  finely  divided  metallic 
copper  to  1086  grams  of  hydrochloric  acid  (sp.  gr.  =  1.124),  the 
mixture  being  slowly  introduced  and  the  acid  frequently  stirred. 
The  copper  powder  is  best  prepared  by  the  reduction  of  copper 
oxide  with  hydrogen.  After  this  mixture  has  been  added  to  the 
acid,  a  spiral  of  copper  wire  reaching  from  the  bottom  of  the 
bottle  up  to  its  neck  is  inserted,  and  the  bottle  is  closed  with  a 
soft  rubber  stopper.  The  solution  is  dark  in  the  beginning,  but 
upon  standing  it  becomes  wholly  colorless.  In  contact  with  the 
air,  however,  it  again  turns  dark  brown,  and  some  cupric  chloride 
forms. 

The  analytical  absorbing  power  of  the  solution  is  4  cc.  of 
carbon  monoxide. 

Another  method  somewhat  more  rapid  and  convenient  than 
that  just  described  is  given  by  Sandmeyer.1 

Twenty-five  parts  of  crystallized  copper  sulphate  and  1 2  parts 
of  dry  sodium  chloride  are  placed  in  50  parts  of  water  and  heated 
until  the  copper  sulphate  dissolves.  Some  sodium  sulphate  may 
separate  out  at  this  point,  but  the  preparation  is  continued 
without  the  removal  of  this  salt.  100  parts  of  concentrated 
hydrochloric  acid  and  13  parts  of  copper  turnings  are  then 
added  and  the  whole  is  boiled  in  a  flask  until  decolorized.  To 
avoid  excessive  evaporation  it  is  desirable  to  insert  in  the  neck 
of  the  flask  a  tall  condensing  tube  or  an  upright  condenser.  The 
addition  of  platinum  foil  to  the  contents  of  the  flask  will  facilitate 
reduction.  The  solution  should  be  kept  in  bottles  that  are 
filled  up  to  the  neck  and  are  closed  by  rubber  stoppers. 

The  ammoniacal  solution  of  cuprous  chloride  may  be  prepared 
as  follows:  — 

800  cc.  of  the  hydrochloric  acid  solution  prepared  by  the 
Winkler  method  given  above  or  1200  cc.  of  the  Sandmeyer 
solution  is  poured  into  about  4  liters  of  water,  and  the  resulting 

1  Berichte  der  deutschen  chemischen  Gesellschaft,  17  (1884),  1633. 


PROPERTIES   OF  THE   VARIOUS   GASES  233 

precipitate  is  transferred  to  a  graduated  stoppered  cylinder  of 
250  cc.  capacity.  After  about  two  hours  the  precipitate  and 
liquid  which  is  above  the  50  cc.  mark  is  drawn  off  by  means 
of  a  siphon  and  7.5  per  cent  ammonium  hydroxide  is  added 
up  to  the  250  cc.  mark.  The  stopper  is  inserted,  the  cylinder  is 
well^  shaken,  and  it  is  then  allowed  to  stand  for  several  hours. 
A  solution  prepared  in  this  manner  has  so  slight  a  tension  that 
the  latter  may  in  nearly  every  case  be  disregarded. 

The  analytical  absorbing  power  of  this  solution  is  6  cc.  of 
carbon  monoxide. 

Frischer  suggests  1  the  preparation  of  an  ammoniacal  solution 
of  a  cuprous  salt  by  adding  ferrous  sulphate  to  an  ammoniacal 
solution  of  cupric  sulphate,  but  he  gives  no  specific  directions. 

Solutions  of  cuprous  chloride  have  no  considerable  tension,  so 
that  this  may  be  disregarded  in  analyses  in  which  only  approxi- 
mate results  are  desired.  In  very  exact  determinations,  however, 
the  gases  that  have  been  in  contact  with  the  reagent  must  be 
freed  from  hydrogen  chloride  or  from  ammonia. 

The  solutions  of  cuprous  chloride  may  conveniently  be  used 
in  the  Hempel  double  pipettes  for  liquid  reagents  (Fig.  36). 

If,  after  the  absorption  of  carbon  monoxide  in  a  gas  mixture, 
the  hydrogen  is  to  be  determined  with  palladium,  the  ammonia- 
cal solution  must  be  used.  If  the  amount  of  carbon  monoxide 
alone  is  to  be  ascertained,  the  hydrochloric  acid  solution  may  be 
employed  with  equally  good  resultSi 

H.  Drehschmidt 2  has  shown,  however,  that  the  union  of 
carbon  monoxide  with  cuprous  chloride  is  so  feeble  that  upon 
shaking  a  solution  that  has  taken  up  any  considerable  quantity 
of  carbon  monoxide,  this  gas  is  again  given  up  in  an  atmosphere 
free  from  carbon  monoxide.  For  this  reason  two  pipettes  are 
used  in  the  absorption,  one  pipette  containing  a  solution  of  cu- 
prous chloride  that  has  been  in  use  some  time,  the  other  a  solution 

1  Chem.  Ztg.,  32  (1908),  1005. 

2  Berichte  der  deutschen  chemischen  Gesellschaft,  2O  (1887),  2344,  2752;  and  21 
(1888),  2158. 


234  GAS  ANALYSIS 

that  has  been  but  little  used.  In  the  absorption,  the  gas  in 
question  is  first  shaken  for  two  minutes  with  the  first-mentioned 
solution,  is  drawn  back  into  the  burette  and  is  then  passed  into 
the  second  pipette  containing  the  but  slightly  used  solution, 
and  is  shaken  three  minutes  therein.  According  to  Drehschmidt, 
the  ammoniacal  solution  is  to  be  preferred  to  the  hydrochloric 
acid  one. 

The  results  obtained  by  Gautier  and  Clausmann  1  in  their 
experiments  on  the  removal  of  carbon  monoxide  by  absorption 
with  cuprous  chloride  demonstrate  the  necessity  of  using  two 
solutions  of  cuprous  chloride  as  Drehschmidt  recommends, 
and  of  shaking  the  gas  with  the  absorbent,  and  furnish 
convincing  evidence  of  the  difficulty  of  effecting  complete 
removal  of  carbon  monoxide  in  the  apparatus  of  Elliott 
or  with  the  form  of  absorption  pipette  customarily  employed  in 
the  Orsat  apparatus.  Producer  gas  contains  a  high  percentage 
of  carbon  monoxide  (sometimes  as  high  as  thirty  per  cent)  and 
a  comparatively  small  amount  of  hydrogen.  In  the  analysis  of 
such  gas  mixtures  it  should  be  borne  in  mind  that  the  analytical 
absorbing  power  of  the  acid  solution  of  cuprous  chloride  is  only 
4,  and  of  the  ammoniacal  solution  of  cuprous  chloride  only  6, 
and  that  the  absorption  of  carbon  monoxide  by  either  of  these 
reagents  becomes  quite  slow  even  before  these  limits  are  reached. 
It  is  consequently  of  particular  importance  that  record  be  kept 
of  the  volume  of  carbon  monoxide  that  the  absorbent  has  taken 
up,  and  that  the  absorbent  be  renewed  as  soon  as  it  has  lost  its 
efficiency. 

Certain  gases  other  than  carbon  monoxide  are  soluble  to  an 
appreciable  degree  in  solutions  of  cuprous  chloride.  This  renders 
it  necessary,  if  accurate  results  are  to  be  obtained,  to  saturate 
the  cuprous  chloride  solution  with  those  gases  that  are  slightly 
soluble  in  it  before  proceeding  to  the  absorption  of  carbon 
monoxide. 

Solutions  of  cuprous  chloride  absorb  not  only  carbon  mon- 

1  Compt.  rend.,  142  (1906),  485. 


PROPERTIES  OF  THE  VARIOUS   GASES  235 

oxide,  oxygen  and  acetylene,  but  also  the  so-called  heavy  hydro- 
carbons. For  this  reason  the  heavy  hydrocarbons,  even  if  their 
determination  is  not  desired,  must  be  removed  from  the  gas  mix- 
ture before  the  carbon  monoxide  is  absorbed  by  cuprous  chloride. 
Failure  to  do  this  is  a  frequent  cause  of  erroneous  results. 

Determination  of  Carbon  Monoxide  by  means  of  Iodine 
Pentoxide.  —  Nicloux  l  and  Gautier  2  employ  the  reaction  be- 
tween iodine  pentoxide  and  carbon  monoxide  (see  p.  231)  for 
the  quantitative  determination  of  the  latter  substance.  Kinni- 
cutt  and  Sanford  3  have  shown  that  this  method  can  be  used  for 
the  determination  of  very  small  amounts  of  carbon  monoxide 
not  only  in  air,  but  also  in  illuminating  gas.  The  gas  mixture 
under  examination  must  first  be  freed  from  unsaturated  hydro- 
carbons, hydrogen  sulphide,  sulphur  dioxide,  and  similar  reduc- 
ing gases.  To  accomplish  this  Kinnicut  and  Sanford  pass  the 
gas  through  two  U-tubes,  one  containing  sulphuric  acid  4  and 
the  other  small  pieces  of  potassium  hydroxide.5  The  purified 
gas  is  then  passed  through  a  small  U-tube  containing  25  grams 
of  iodine  pentoxide.  Inasmuch  as  this  substance  acts  upon 
cork,  rubber,  and  the  usual  lubricants,  Morgan  and  McWhorter 
later  suggested 6  that  the  iodine  pentoxide  be  placed  in  a  U-tube 
with  side  arms,  and  that  the  large  ends  of  the  U-tube  be  then 
sealed  before  the  blast  lamp.  The  U-tube  is  suspended  in  an  oil 
bath  and  its  exit  tube  is  joined  to  a  Wolff  absorption  tube  (see 
page  228)  containing  0.5  grams  of  potassium  iodide  dissolved  in 
5  cc.  of  water.  The  oil  bath  is  heated  to  150°  C.  The  tempera- 
ture should  not  be  allowed  to  rise  much  beyond  150°  C.,  for 
Nowicki7  has  found  that  iodine  pentoxide  itself  begins  to  de- 

1  Compt.  rend.,  126  (1898),  746. 
*Ibid.,  126  (1898),  931. 

3  /.  Am.  Chem.  Soc.,  22  (1900),  14. 

4  It  would  be  preferable  to  place  the  sulphuric  acid  in  a  Friedrichs  spiral  gas  wash- 
ing bottle  (see  p.  123). 

5  See  also  Weiskopf,  /.  Chem.  Met.  Soc.  S.  Africa,  g  (1909),  258,  306. 

6  J.  Am.  Chem.  Soc.,  29  (1907),  1589. 

7  Oesterr.  Zeit.f.  Berg-HiM,  54  (1906),  6. 


236  GAS  ANALYSIS 

compose  at  165°  and  is  completely  broken  down  at  300°.  He 
also  states  that  the  oxidation  of  carbon  monoxide  by  iodine 
pentoxide  begins  at  45°  and  is  complete  at  88°.  From  250  cc.  to 
1000  cc.  of  the  gas  mixture  under  examination  is  then  passed 
through  the  apparatus  at  the  rate  of  about  one  liter  in  two  hours. 
The  iodine  that  is  set  free  in  the  reaction  is  absorbed  by  the 
solution  of  potassium  iodide  in  the  Wolff  tube. 

Kinnicut  and  Sanford  determined  the  amount  of  carbon 
monoxide  in  the  gas  mixture  by  titrating  the  free  iodine  with 
N/IOOO  solution  of  sodium  thiosulphate;  0.002266  gram  of 
iodine  is  equivalent  to  one  cc.  of  carbon  monoxide  measured 
under  standard  conditions. 

In  the  reaction  between  iodine  pentoxide  and  carbon  monox- 
ide, one  cc.  of  carbon  monoxide  yields  one  cc.  of  carbon  dioxide 
which  in  the  above  method  passes  through  the  solution  of 
potassium  iodide.  Morgan  and  McWhorter  1  recommend  that 
as  a  check  upon  or  substitute  for  the  iodine  titration,  the  liber- 
ated carbon  dioxide  be  determined.  This  they  do  by  passing  the 
gas  that  issues  from  the  Wolff  tube  through  an  absorption 
apparatus  2  containing  50  cc.  of  a  solution  of  barium  hydroxide 
such  as  is  used  in  the  Hesse  method  for  the  determination  of 
carbon  dioxide  in  air,  and  determining  the  volume  of  the  ab- 
sorbed carbon  dioxide  by  titration  with  a  standard  solution  of 
oxalic  acid  that  contains  1.1265  grams  of  crystallized  oxalic  acid 
to  the  liter.  Five  cc.  of  this  solution  is  equivalent  to  one  cc.  of 
carbon  dioxide  measured  under  standard  conditions.  Phenol- 
phthalein,  one  part  in  250  parts  of  alcohol,  is  used  as  indicator. 

The  above  method  for  the  determination  of  carbon  monoxide 
by  the  use  of  iodine  pentoxide  gives  very  accurate  results  if  the 

1  Loc.  cit. 

2  They  used  a  long  test  tube  (24  x  2.5  cm.).    This  might  advantageously  be  re- 
placed by  a  glass  cylinder  about  20  cm.  high  and  4  cm.  internal  diameter,  fitted 
with  a  three-hole  rubber  stopper  carrying  an  inlet  and  exit  tube,  and  the  tip  of  a 
burette.     Such  an  arrangement  would  permit  of  the  titration  of  the  solution  of 
barium  hydroxide  without  transferring  it  to  another  container  and  thus  exposing  it 
to  the  air. 


PROPERTIES   OF  THE   VARIOUS   GASES  237 

carbon  monoxide  is  present  in  quite  small  amounts.  By  means 
of  it  one  part  of  carbon  monoxide  in  40,000  parts  of  air  may  be 
determined  in  as  small  an  initial  volume  of  air  as  one  liter.  It  is, 
however,  not  suited  to  the  determination  of  large  amounts  of 
carbon  monoxide  as  Gill  and  Bartlett  have  shown  l  in  their 
examination  of  the  method  of  Smits,  Raken  and  Torwogt 2  who 
had  proposed  the  employment  of  the  method  for  the  determina- 
tion of  carbon  monoxide  in  illuminating  gas. 

Colorimetric  Determination  of  Carbon  Monoxide.  —  Hal- 
dane  has  devised  3  a  colorimetric  method  for  the  determination 
of  small  amounts  of  carbon  monoxide  in  air.  The  method  is 
based  upon  the  fact  that  when  oxygen  and  carbon  monoxide  are 
passed  through  a  blood  solution  the  amounts  of  oxyhaemoglobin 
and  carbon  monoxide  haemoglobin  that  are  formed  are  in  the 
ratio  of  the  partial  pressures  of  these  two  gases  in  the  air,  multi- 
plied by  a  constant.  The  percentage  of  oxygen  in  the  gas  mix- 
ture can  easily  be  determined  by  analysis,  and  if  the  value  of 
the  constant  is  known,  the  percentage  of  carbon  monoxide  in 
the  gas  can  then  be  calculated  from  the  relative  amounts  of 
oxyhaemoglobin  and  carbon  monoxide  haemoglobin  that  are 
formed  in  a  solution  of  blood  through  which  the  gas  mixture 
in  question  has  been  passed. 

A  dilute  solution  of  oxyhaemoglobin  is  of  a  yellow  color,  while 
that  of  carbon  monoxide  haemoglobin  is  pink.  The  two  solu- 
tions required  for  the  colorimetric  determination  are  —  (i)  A  five 
per  cent  solution  of  defibrinated  blood/  This  solution  should 
be  freshly  prepared  and  should  be  kept  in  a  stoppered  bottle. 
(2)  A  solution  of  carmine,  which  is  prepared  by  grinding  one 
gram  of  carmine  with  a  few  drops  of  ammonium  hydroxide  in 
a  mortar  and  dissolving  the  substance  in  100  cc.  of  glycerine. 
Ten  cc.  of  this  liquid  diluted  to  one  liter  with  water  forms  the 
standard  solution. 

1  J.  Ind.  and  Eng.  Chem.,  2  (1910),  9. 

2  Z.f.  angew.  Chem.,  1900,  1002. 

3  /.  Physiol.,  18  (1895),  461. 


238  GAS  ANALYSIS 

The  air  under  examination  is  drawn  through  a  bottle  of 
about  200  cc.  capacity  fitted  with  a  three-hole  rubber  stopper. 
In  two  of  the  openings  of  the  stopper  are  inserted  the  inlet  and 
outlet  tubes  for  the  passage  of  the  air,  and  the  third  is  closed 
by  a  glass  plug.  After  the  air  originally  in  the  bottle  has  been 
completely  displaced  by  the  air  under  examination,  the  rubber 
tubes  attached  to  the  glass  tubes  of  the  bottle  are  closed  by  pinch- 
cocks.  The  glass  rod  closing  the  third  opening  in  the  stopper 
is  then  removed,  and  there  is  inserted  through  this  opening 
the  tip  of  a  small  pipette  that  contains  about  five  cc.  of  the 
blood  solution.  This  solution  is  allowed  to  run  down  into  the 
bottle,  the  pipette  is  withdrawn,  the  opening  in  the  stopper 
is  again  closed  with  a  plug,  and  the  flask  is  gently  shaken  for 
about  five  minutes. 

The  blood  solution  is  then  transferred  to  a  small  colorimeter 
tube.  In  a  second  colorimeter  tube  of  exactly  the  same  dimen- 
sions, five  cc.  of  the  original  blood  solution  is  placed,  and  in  a 
third  tube  five  cc.  of  the  blood  solution  that  has  been  saturated 
with  carbon  monoxide  by  shaking  the  blood  with  coal  gas. 
The  standard  carmine  solution  is  now  run  from  a  burette  into 
the  second  colorimeter  tube  until  the  color  of  the  liquid  is 
identical  with  that  of  the  solution  that  has  been  saturated 
with  carbon  monoxide.  The  carmine  solution  is  then  added 
to  the  contents  of  the  first  test  tube  until  the  same  tint  is 
produced. 

If  x  cc.  of  the  carmine  solution  were  run  into  a  second  tube, 
and  y  cc.  into  the  first  tube,  then 


x  +  5 
X  *  x  zoo  =  5, 


y  +5 


in  which  5  is  the  percentage  saturation  of  the  blood  that  has 
been  shaken  with  the  air  under  examination.  The  amount  of 
carbon  monoxide  in  the  air  may  then  be  calculated  from  the  fol- 
lowing table: 


PROPERTIES   OF  THE   VARIOUS   GASES 


239 


PERCENTAGE  SATURATION 

CARBON  MONOXIDE  IN  AIR 

10 

0.015  per  cent 

20 

0.04 

30 

0.08 

40 

O.I2 

SO 

0.16 

60 

O.22 

70 

0.30 

80 

O.6O 

90 

1.2 

The  method  is  stated  to  give  fairly  accurate  results  for  amounts 
of  carbon  monoxide  in  air  between  0.015  and  one  per  cent.  With 
more  than  one  per  cent  of  carbon  monoxide  the  gas  should  be  di- 
luted with  air  that  is  free  from  carbon  monoxide. 

Determination  of  Carbon  Monoxide  by  Fractional  Com- 
bustion. —  Nesmjelow  1  has  made  an  exhaustive  study  of  the 
fractional  combustion  of  carbon  monoxide  in  the  presence  of 
hydrogen  and  methane.  He  summarizes  the  results  of  his  ex- 
periments as  follows:  — 

(1)  That  when  hydrogen  mixed  with  air  is  passed  through  a 
U-shaped  tube  that  contains  palladium  asbestos  and  stands  at 
the  temperature  of  the  room,  the  hydrogen  is  burned  completely 
upon  a  single  passage  of  the  gas  mixture  through  the  tube; 

(2)  That  when  a  mixture  of  hydrogen,  carbon  monoxide  and 
air  is  passed  through  the  U-tube,  both  the  hydrogen  and  carbon 
monoxide  (in  the  proportions  in  which  he  used  them)  burn  com- 
pletely without  previous  warming  of  the  palladium  asbestos. 
It  is  thus  easily  possible  to  determine  hydrogen  and  carbon 
monoxide  by  combustion  over  palladium  asbestos,  and  ascer- 
taining the  contraction  and  the  volume   of   carbon   dioxide 
formed; 

(3)  That  the  combustion  of  carbon  monoxide  under  the  above 
conditions  begins  at  1 20°,  while  that  of  methane  does  not  begin 

1  Z.  analyt.  Ch.,  48  (1009),  232. 


240  GAS  ANALYSIS 

below  150°,  and  that  if  a  mixture  of  hydrogen,  carbon  monoxide, 
methane  and  air  is  passed  through  the  palladium  asbestos  tube, 
at  a  speed  not  exceeding  one  liter  per  hour,  hydrogen  and  car- 
bon monoxide  will  be  completely  oxidized  and  methane  will 
not  be  attacked.  If  the  speed  of  flow  of  the  gas  mixture  be  in- 
creased, the  rise  of  temperature  in  the  U-tube,  resulting  from 
the  more  active  combustion,  may  cause  some  of  the  methane 
to  burn  and  thus  render  the  results  worthless. 

Nesmjelow  then  describes  a  method,  original  with  him,  for  the 
fractional  combustion  of  carbon  monoxide  by  means  of  copper 
oxide.  Copper  oxide,  mixed  with  asbestos  fibers,  is  heated  to 
dark  redness  and,  after  cooling  in  a  desiccator,  is  placed  in  a 
small  U-tube  of  hard  glass.  This  is  connected  at  the  two  ends 
with  a  gas  burette  and  pipette  in  the  usual  manner,  and  a  sand 
bath  is  then  brought  up  under  it  and  the  lower  part  of  the  tube 
is  covered  with  the  sand.  The  bath  is  heated  to  250°,  and  the 
mixture  of  hydrogen,  carbon  monoxide,  methane  and  air  passed 
through  it  about  six  times.  The  sand  bath  is  then  removed 
and  the  gas  cooled  to  the  temperature  that  it  had  at  the  begin- 
ning. The  volume  is  measured  and  then  the  carbon  dioxide 
that  has  been  formed  is  determined  by  absorption.  From  these 
data  the  carbon  monoxide  and  the  hydrogen  (which  of  course 
burns  also)  are  calculated.  At  the  above  temperature  methane 
is  not  oxidized.  The  speed  of  flow  of  the  gases  through  the 
U-tube  has  no  effect  upon  the  accuracy  of  the  separation. 

METHANE  (CH4) 

Marsh-gas  —  Fire-damp 

Properties  of  Methane.  —  Specific  gravity,  0.5539;  weight 
of  one  liter,  0.7160  gram. 

According  to  Bunsen,  i  volume  of  water  absorbs  at  a  tempera- 
ture /, 

0.05449  —  0.0011807  t  +  0.000010278  t2; 


PROPERTIES  OF  THE  VARIOUS   GASES  241 

hence  at  20°,  0.03499  volume. 

One  volume  of  alcohol  absorbs  at  temperature  /, 

0.522586  —  0.0028655  /  +  0.0000142  t2; 
hence   at  20°,  0.47096  volume. 

Determination  of  Methane.  —  Methane  may  be  determined 
by  explosion  with  oxygen  or  air  (see  p.  141),  by  combustion  with 
copper  oxide  (see  p.  200),  by  combustion  in  the  Drehschmidt 
platinum  capillary  tube  (see  p.  154)  or  by  combustion  in  the 
Dennis  pipette  (see  p.  148). 

(i)  CH4  +  2  O2  =  CO2  +  2  H20 

i  vol.     2  vol.     I  vol.     liquid 

The  amount  of  methane  may  be  ascertained  either  by  deter- 
mining the  volume  of  carbon  dioxide  that  is  formed,  which 
will  equal  the  volume  of  the  methane,  or  by  absorbing  the 
carbon  dioxide  without  measuring  it  and  ascertaining  the  to- 
tal diminution  in  volume,  J  of  which  will  equal  the  volume  of  the 
methane. 

In  the  opinion  of  the  author  the  method  of  determining  meth- 
ane with  the  combustion  pipette  is  superior  (a)  to  the  explo- 
sion method  because  it  permits  of  the  combustion  of  the  total 
residue  and  avoids  the  possibility  of  error  through  formation 
of  oxides  of  nitrogen;  (b)  to  the  combustion  with  copper  oxide 
because  the  latter  calls  for  high  and  prolonged  heating  of  the 
combustion  tube;  (c)  and  to  the  combustion  with  the  Dreh- 
schmidt capillary  because  this  method  necessitates  the  use  of  a 
comparatively  large  volume  of  an  explosive  gas  mixture,  and 
further  because  of  the  tendency  of  the  Drehschmidt  tube  to 
show  leakage  after  a  short  period  of  use. 

The  combustion  pipette  and  its  level-bulb  may  be  filled  with 
water  if  no  gases  other  than  methane  and  nitrogen  are  present 
in  the  gas  mixture;  the  methane  is  here  determined  by  passing 
the  gases,  after  combustion,  into  a  potassium  hydroxide  pi- 


242  GAS   ANALYSIS 

pette  to  completely  remove  the  carbon  dioxide  and  then  cal- 
culating the  methane  from  the  total  diminution  in  volume  (see 
above). 

If  the  combustion  pipette  and  its  level-bulb  are  filled  with 
mercury  and  the  gases  are  measured  over  mercury,  then  hydro- 
gen, methane  and  nitrogen  may  be  determined  simultaneously 
by  a  single  combustion  by  measuring  the  contraction  after  com- 
bustion and  the  volume  of  carbon  dioxide  that  is  formed. 

A  measured  volume  of  the  gas  mixture  is  transferred  to  the 
combustion  pipette  and  is  burned  in  the  usual  manner  by  the 
slow  addition  of  a  measured  amount  of  oxygen  (see  p.  149). 
The  residual  gas  is  then  passed  back  into  the  burette  and  the 
contraction  in  volume  is  measured.  The  gas  mixture  is  next 
passed  into  the  potassium  hydroxide  pipette  to  absorb  the 
carbon  dioxide  and  is  then  again  drawn  back  into  the  burette 
and  measured. 

Since  one  volume  of  methane  produces,  on  combustion,  one 
volume  of  carbon  dioxide  (see  Equation  i),  the  volume  of  the 
methane  in  the  gas  mixture  is  equal  to  the  volume  of  carbon 
dioxide  formed. 

Since 

(2)  2  H2  +  O2  =2  H2O, 

2  vols.      i  vol.     liquid 

the  contraction  due  to  the  combustion  of  hydrogen  is  equal  to 
f  the  volume  of  hydrogen  in  the  gas  mixture.  The  contraction 
due  to  the  combustion  of  methane  (see  Equation  i)  is  equal  to 
twice  the  volume  of  the  carbon  dioxide  formed.  Consequently 
the  total  contraction  in  the  gas  volume  that  results  when  a  mix- 
ture of  hydrogen  and  methane  is  burned  may  be  represented 
by  the  expression 

Contraction  =  f  H2  +  2  CO2 
or  f  H2  =  Contraction  —  2  CO2 

or  vol.  H2  =  f  (Contraction  —  2  C02) 


PROPERTIES   OF  THE   VARIOUS   GASES 


243 


The  volume  of  hydrogen  in  the  gas  mixture  is  therefore  found 
by  subtracting  twice  the  volume  of  carbon  dioxide  formed  in 
the  combustion  from  the  total  contraction,  and  taking  f  of  the 
remainder. 

The  following  analyses,  taken  from  actual  practice,  show  the 
order  in  which  the  various  measurements  are  made,  and  illus- 
trate the  accuracy  of  the  determination  with  the  combustion 
pipette. 


I 

II 

III 

IV 

V 

Gas  residue  taken                             .      . 

cc. 
61  .4 
98.5 
159-9 
58.8 

101  .1 

34.3 
24.5 

Per  cent 
56.4 
39-9 
3-7 

cc. 

64.50 

96.55 
161.05 

54.95 

106.10 

29.15 
25.80 

Per  cent 
56.30 
40.00 
3-70 

cc. 
67.00 

98.55 
165-55 
55-30 

110.25 

28.60 
26.70 

Per  cent 
56.60 
39-90 
3-50 

cc. 
64.0 
97-6 
161.6 
56.3 
105-3 

30.7 
25-6 

Per  cent 
56.4 
40.0 
3-6 

cc. 

65-7 

IOO.O 

165.7 

57-6 
108.1 

3i-4 
26.2 

Per  cent 
56-5 
39-9 
3-6 

Oxygen  taken 

Total       
Residue  after  combustion    .... 
Contraction    
Residue  after  absorbing  CO2  in  KOH 
pipette  ,  _  7  . 
Carbon  dioxide  found                         /  . 

Hydrogen       .     

Methane  

Nitrogen  (diff  )                                 . 

Hydrogen,  methane,  carbon  monoxide  and  nitrogen  may  be 
determined  by  a  single  combustion  if,  in  addition  to  the  meas- 
urement of  the  total  contraction  and  of  the  volume  of  carbon 
dioxide  formed,  the  volume  of  oxygen  consumed  in  the  combus- 
tion is  ascertained. 

The  combustion  is  carried  on  exactly  in  the  manner  described 
above  for  a  mixture  of  hydrogen,  methane  and  nitrogen  except 
that  after  the  carbon  dioxide  has  been  absorbed  and  the  residue 
measured,  the  excess  of  oxygen  is  determined  by  passing  the  gas 
residue  into  a  pipette  containing  alkaline  pyrogallol  or  sodium 
hyposulphite  and  subtracting  this  result  from  the  total  volume 
of  oxygen  added.  The  difference  is  the  oxygen  consumed  in  the 
combustion.  Having  thus  ascertained  the  contraction  resulting 
from  the  combustion,  the  volume  of  carbon  dioxide  formed,  and 


244  GAS  ANALYSIS 

the  amount  of  oxygen  consumed,  we  have  all  the  data  necessary 
for  the  calculation  of  the  amounts  of  carbon  monoxide,  hydrogen, 
methane  and  nitrogen  existing  in  the  original  mixture. 

The  volume  changes  that  result  from  the  combustion  of 
hydrogen  and  methane  are  shown  in  Equations  i  and  2  on 
pages  241  and  242.  When  carbon  monoxide  is  burned,  two  vol- 
umes of  the  gas  unite  with  one  volume  of  oxygen  to  form  two 
volumes  of  carbon  dioxide. 

(3)  2  CO  +  02  =  2  C02. 

2  VOls.       I  Vol.       2  V01S. 

From  these  three  equations  the  following  expressions  may  be 
derived: 

Contraction  =  %  CO  +  f  H2  +  2  CH4. 
Carbon  dioxide  formed  =  CO  +  CH4. 
Oxygen  consumed  =  i  CO  +  i  H2  +  2  CH4. 

From  these  last  three  equations  a  variety  of  formulas  for  the 
calculation  of  the  various  components  of  the  original  mixture 
may  be  derived.  Noyes  and  Shepard  give  — 

(1)  H2      =  Contraction  minus  oxygen  consumed. 

(2)  CO     =  |  (2  CO2  +  -J-  H2  minus  oxygen  consumed). 

(3)  CH4  =  CO2  —  CO. 

(4)  N2      =  Original  volume  —  (H2  +  CO  +  CH4). 
Instead  of  (2)  and  (3)  we  may  also  use  — 

CO   =  CO2  —  CH4. 

OTT       2  Contraction  —  CO2  —  3  H2. 
CH4=  

3 

If  no  nitrogen  is  present  in  the  original  mixture  the  following 
equations  of  Vignon  may  be  employed,  V  representing  the  vol- 
ume of  the  gas  mixture  taken  for  the  combustion. 


PROPERTIES   OF  THE   VARIOUS   GASES 


245 


H2      =  V  —  CO2. 

CO     =  i  CO2  +  V  —  f  contraction. 
CH4  =  f  CO2  +  f  contraction  —  V. 

The  following  analyses,  taken  from  actual  practice,  illustrate 
the  determination  of  carbon  monoxide,  hydrogen  and  methane 
by  this  method.  The  determination  of  nitrogen  "  by  difference," 
after  the  removal  of  the  absorbable  and  combustible  constitu- 
ents, does  not  yield  accurate  results.  It  is  distinctly  preferable 
to  ascertain  directly  the  amount  of  nitrogen  in  the  gas  mixture 
by  the  method  outlined  on  p.  317. 


I 

II 

III 

IV 

cc. 

cc. 

cc. 

cc. 

Volume  of  gas  residue  taken    . 

83  45 

85.05 

83  05 

86.Q5 

Oxygen  added  

97-65 

96.25 

97.90 

99-95 

Total    . 

181.10 

181.30 

180.95 

186.90 

Volume  after  combustion 

49-30 

46.95 

49-75 

49-50 

Contraction  resulting   from   com- 

bustion   

131  80 

134  35 

131.20 

137  40 

Volume  after  absorption  of  carbon 

dioxide     .            

13-05 

10.15 

13-75 

12.  OO 

Volume  of  carbon  dioxide  formed 

in  the  combustion    .... 

36.25 

36.80 

36.00 

37  50 

Volume  after  absorption  of  excess  of 

oxygen      ........ 

2-53 

2.60 

2-45 

2.62 

Oxygen  in  excess    

10.52 

7-55 

11.30 

9-38 

Oxygen  consumed  in  combustion 

of  CO,  H2,  and  CH4    ...     . 

87-13 

88.70 

86.60 

90  57 

From  the  above  experimental  results  the  calculated  percent- 
ages of  the  various  gases  are  as  follows:  — 


I 

II 

in 

IV 

Carbon  monoxide 

Per  cent 
6  2 

Per  cent 

6  i 

Per  cent 
6   2 

Per  cent 

6  o 

Hydrogen  
Methane  , 
Nitrogen  (difference)  .... 

53  5 
37  3 
30 

53  7 
37-2 
30 

53  7 
37-2 
2.9 

53  9 
37-i 
30 

246  GAS  ANALYSIS 

In  a  recent  article  x  Hempel  states  that  he  has  found  it  difficult 
to  obtain  complete  combustion  of  methane  with  the  Dennis 
combustion  pipette  when  methane  is  mixed  with  nitrogen.  He 
asseverates  that  when  the  ordinary  procedure  is  followed,  a  part 
of  the  methane  may  escape  combustion,  and  that  for  complete 
combustion  it  is  necessary  to  maintain  the  spiral  at  red  heat  for 
a  considerable  length  of  time,  which  causes  surface  oxidation  of 
the  mercury  in  the  pipette,  and,  as  a  consequence,  too  high  con- 
traction. There  is  no  doubt  that  this  error  would  result  if  the 
spiral  were  subjected  to  prolonged  heating,  but  experience  of 
several  years  with  the  combustion  pipette  leads  the  author  to 
believe  that  the  maintenance  of  the  spiral  at  red  heat  for  sixty 
seconds  after  the  introduction  of  the  gas  suffices  in  all  cases  for 
complete  combustion  of  the  methane,  a  statement  that  seems  to 
be  borne  out  by  the  analyses  given  on  pages  243  and  245  and 
many  others  that  might  be  cited.  When  the  spiral  is  heated  for 
so  brief  a  time  no  appreciable  oxidation  of  the  mercury  in  the 
pipette  results. 

THE  HEAVY  HYDROCARBONS 

As  used  in  technical  gas  analysis,  the  term  "heavy  hydro- 
carbons" comprises  gases  of  the  series  CnH2n  (the  olefines), 
such  as  ethylene,  C2H4,  propylene,  C3H6,  and  butylene,  C4Hs; 
of  the  series  CnH^n  _  2,  such  as  acetylene,  C2H2;  and  of  the  series 
CnH2n_6,  such  as  benzol  (benzene),  C6H6,  and  toluol  (toluene) 
C7H8. 

The  heavy  hydrocarbons  are  the  chief  illuminants  in  coal  gas 
or  carburetted  gas,  and  for  this  reason  their  determination  is  of 
importance  when  the  gas  is  to  be  used  directly  for  illuminating 
purposes . 

Absorption  of  Heavy  Hydrocarbons. — All  of  these  gases  are 
absorbed  by  fuming  sulphuric  acid  of  about  1.94  specific  gravity 
containing  about  24%  free  sulphur  trioxide  at  15°.  The  acid 
is  placed  in  a  special  absorption  pipette  of  the  form  shown  in 

1  Zeit.f.  angew.  Ghent.,  36  (1912),  1841. 


PROPERTIES   OF   THE   VARIOUS   GASES 


247 


Fig.  86.    The  small  upper  absorption  bulb  B  is  about  5  cm.  in 

diameter  and  is  filled  by  the  glass-blower  with  pieces  of  broken 

glass  which  serves  to  increase  the  surface  of  contact  between  the 

gas  and  the  acid.    When  broken  glass  is  used  in  gas  pipettes 

there  is  danger  that  some  gas  may  be  trapped  between  the  pieces 

of  glass.    This  may  usually  be 

avoided  by  drawing  up  the  liq- 

uid very  slowly  in  the  bulb  that 

contains  the  broken  glass.    The 

fuming  sulphuric  acid  is  intro- 

duced into  the  pipette  through 

A.    When  the  pipette  is  not  in 

use  A  and  C  are  covered  with 

small    glass    caps    made    from 

glass  tubing. 

To  effect  the  removal  of  the 
heavy  hydrocarbons,  the  glass 
caps  on  the  pipette  are  removed, 
and  a  short  piece  of  small  rubber 
tubing,  such  as  is  used  on  the 
other  gas  pipettes,  is  slipped 
upon  C.  A  pinchcock  is  placed 
upon  this  rubber  tube.  The  acid 

in  the  pipette  is  driven  up  in  the  capillary  to  the  point  marked 
H  by  blowing  through  a  rubber  tube  that  has  been  attached  to 
the  end  A,  and  the  pinchcock  is  closed.  The  pipette  and  gas 
burette  are  then  connected  by  an  empty,  dry  capillary  tube  of 
the  usual  form.  The  gas  mixture  is  then  slowly  passed  over  into 
the  pipette,  and  after  a  few  seconds  is  slowly  drawn  back  into 
the  burette.  This  is  repeated  three  times  or  more,  the  number 
of  passages  of  the  gas  depending  upon  the  per  cent  of  the  heavy 
hydrocarbons  present  and  the  strength  of  the  acid.  Throughout 
the  operation  the  fuming  sulphuric  acid  should  never  be  drawn 
above  the  point  H  in  the  capillary  of  the  pipette.  When  the  gas 
is  drawn  back  into  the  burette  the  last  time,  the  acid  in  the 


JTIG 


248  GAS  ANALYSIS 

pipette  should  be  brought  exactly  to  the  point  H.  The  pinch- 
cock  at  the  top  of  the  burette  is  now  closed.  The  diminution 
in  the  gas  volume  may  not  yet  be  read  off  on  the  burette  because 
of  the  presence  in  the  gas  of  sulphur  trioxide  from  the  fuming 
acid  in  the  pipette.  This,  together  with  any  sulphur  dioxide 
that  may  have  been  formed  during  the  absorption,  is  removed 
by  passing  the  gases  into  a  pipette  filled  with  potassium  hy- 
droxide (see  p.  225).  Then  gas  is  then  drawn  back  into  the  bu- 
rette and  the  decrease  in  volume  noted. 

The  moisture  content  of  the  gas,  after  it  has  been  brought 
into  contact  with  the  fuming  sulphuric  acid  and  the  potassium 
hydroxide,  will  of  course  be  less  than  at  the  beginning  of  the 
determination  when  the  gas  was  "saturated"  with  water  vapor. 
To  avoid  error  from  this  cause  in  the  final  measurement  the 
gas  must  in  this,  as  in  all  other  similar  absorptions,  finally  be 
read  over  water  or  over  mercury  upon  which  stands  a  drop  of 
water. 

This  method  of  manipulation  introduces  slight  errors  in  the 
results  for  those  gases  that  are  determined  after  the  heavy 
hydrocarbons  are  removed,  because  the  connecting  capillary 
tube  and  the  upper  part  of  the  capillary  of  the  pipette  are  filled 
with  air  when  the  burette  and  pipette  are  connected.  The 
volume  of  air  in  the  capillaries  is,  however,  so  small 1  that  the 
errors  arising  from  this  source  may  be  disregarded  in  technical 
analyses. 

ETHYLENE  (^H^) 

Properties  of  Ethylene.  — Specific  gravity,  0.9684;  weight 
of  one  liter,  1.2520  grams. 

One  volume  of  water  absorbs  at  temperature  /, 

0.25629  —  0.00913631  t  +  0.000188108  t2', 
hence  at  20°,  0.1488  volume  (Bunsen). 

1  The  length  of  the  empty  capillary  tube  need  not  exceed  16  cm.  which  has  a 
volume  of  only  0.16  cc. 


PROPERTIES  OF  THE  VARIOUS   GASES  249 

One  volume  of  alcohol  absorbs  at  t°, 

3.59498  —  0.057716  i  +  0.0006812  t2; 

hence  at  20°,  2.7131  volumes  (Carius). 

Ether  absorbs  about  twice  its  volume,  turpentine  oil  and  pe- 
troleum two  and  a  half  times  their  volumes,  and  olive  oil  its 
own  volume  of  ethylene. 

Determination  of  Ethylene  by  Absorption. —  Bromine  water 
absorbs  the  gas  rapidly  and  completely; l  the  vapor  of  bromine 
must  be  removed  after  the  absorption  by  passing  the  gas  into  a 
potassium  hydroxide  pipette.  The  reagent  is  prepared  by  dilut- 
ing saturated  bromine  water  with  twice  its  volume  of  water.  It 
then  contains  about  one  per  cent  of  bromine.  The  liquid  is 
placed  in  a  Hempel  double  absorption  pipette  for  liquid  reagents 
(Fig.  36)  with  water  in  the  last  two  bulbs. 

The  usual  absorbent  for  ethylene  is  fuming  sulphuric  acid, 
ethionic  acid,  C2H6S2O7,  being  formed.  The  determination  is 
carried  out  in  the  manner  described  on  p.  247. 

Determination  of  Ethylene  in  presence  of  Acetylene.  — 
Tucker  and  Moody  state  2  that  ethylene  may  be  determined  in 
mixture  with  acetylene  by  passing  the  gases  through  an  ammoni- 
acal  silver  solution  which  removes  acetylene  completely  but  ab- 
sorbs only  a  relatively  small  amount  of  ethylene.  The  method  is 
not  exact  but  it  might  prove  useful  in  an  approximation  of  the 
percentages  of  ethylene  and  acetylene  in  a  mixture  of  the  two 
gases.  The  ammoniacal  silver  solution  that  is  used  in  this  sep- 
aration is  prepared  by  dissolving  10  grams  of  silver  nitrate  in 
500  cc.  of  distilled  water,  adding  dilute  hydrochloric  acid  until 
the  solution  is  barely  acid  to  litmus  paper,  and  then  adding  am- 
monium hydroxide  until  the  solution  is  slightly  ammoniacal. 
When  acetylene  is  absorbed  by  this  solution,  silver  acetylide, 
Ag2C2,  is  formed. 

1  Treadwell  and  Stokes,  Berichte  der  deutschen  chemischen  Gesettschaft,  21  (1888), 
3131;  Haber  and  Oechelhauser,  ibid.,  29  (1896),  2700. 

2  J.  Am.  Chem.  Soc.,  23  (1901),  671. 


250  GAS  ANALYSIS 

Separation  of  Ethylene  from  Benzene.  —  The  separation 
of  ethylene  from  benzene  may,  according  to  Haber  and  Oechel- 
hauser,1  be  accomplished  by  means  of  bromine  water  which 
removes  the  ethylene  completely  but  does  not  appreciably 
attack  the  benzene  if  the  contact  between  gas  and  reagent  is  not 
prolonged  beyond  two  minutes.  Some  benzene  vapor  is,  how- 
ever, mechanically  carried  down  by  the  bromine  vapor,  and  for 
this  reason  the  method  does  not  yield  very  accurate  results. 

Separation  of  Ethylene  from  Butylene.  —  Fritzsche  states  2 
that  ethylene  may  be  volumetrically  separated  from  butylene 
by  means  of  sulphuric  acid  of  1.62  specific  gravity  which  absorbs 
butylene  but  not  ethylene. 

PROPYLENE  (C3H6) 

Specific  gravity,  1.4527;  weight  of  one  liter,  1.878  grams. 

The  gas  may  be  determined  by  absorption  with  fuming  sul- 
phuric acid  or  by  combustion.  Details  of  these  methods  are 
given  on  pages  247  and  149. 

ACETYLENE 

Properties  of  Acetylene.  —  Specific  gravity,  0.8988;  weight 
of  one  liter,  1.1620  grams. 

Acetylene  is  quite  soluble  in  a  number  of  liquids,  as  is  shown 
in  the  following  table:  3 

at  12°  and  755  mm. 

i  vol.  saturated  salt  solution  dissolves  o .  23  vol.  acetylene 
i    "     water  "        1.18    "  " 

at  1 8°  and  760  mm. 

i  vol.  carbon  disulphide  dissolves      i .  o  vol.  acetylene 
i    "     oil  of  turpentine  "  2.0"          " 

i    "     carbon  tetrachloride  2.0      "          " 

1  /./.  Gasbdeuchtung,  39  (1896),  799;  43  (1900),  347. 

2  Z.f.  angew.  Chem.,  1896,  456. 

3  Vogel,  Handbuchfiir  Acetylen,  p.  152. 


PROPERTIES  OF  THE   VARIOUS   GASES  251 

at  18°  and  760  mm. 

vol.  amyl  alcohol  dissolved      3 . 5  vol.  acetylene 

"     styrol  3-5      " 

"     chloroform  4.0      " 

"     benzene  4.0      " 

"     absolute  alcohol  "           6.0     " 

acetic  acid  6.0      " 

"     acetone  25                     " 

at  15°  and  12  atm. 
i    "     acetone  "       300      vol.  acetylene 

at  —  80°  and  760  mm. 
i    "     acetone  "     2000      vol.  acetylene 

It  is  slowly  absorbed  by  concentrated  sulphuric  acid,  acetyl 
sulphonic  acid,  C2H4SO4,  being  formed.  An  ammoniacal  solu- 
tion of  cuprous  chloride  absorbs  the  gas  rapidly  and  there  is 
formed  a  brown  to  violet-red  precipitate  of  copper  acetylide, 
Cu2C2,  which  explodes  when  heated  or  struck.  Acetylene 
produces  in  an  ammoniacal  silver  solution  1  a  white  precipitate, 
Ag2C2,  which  is  even  more  explosive  than  the  copper  acetylide. 
If  the  gas  is  led  into  ammoniacal  solutions  of  aurous  thiosulphate 
or  potassium  mercuric  iodide,  exceptionally  explosive  com- 
pounds are  formed. 

All  of  the  ammoniacal  solutions  of  metals  that  have  been 
mentioned  may  be  used  as  absorbents  for  acetylene, 

Determination  of  Acetylene.  —  Although  acetylene  may  be 
determined  by  combustion  with  oxygen,  this  method  cannot 
usually  be  employed  because  the  gas  occurs  in  mixtures  with 
other  combustible  gases.  One  volume  of  acetylene  yields  on 
combustion  2  volumes  of  carbon  dioxide.  When  2  volumes  of 
acetylene  are  burned  there  is  a  contraction  of  3  volumes. 

2  C2H2  +  5  O2      =  4  CO  2  +  2  H2O. 
2  vols.        5  vols.      4  vols.       liquid. 

1  The  method  of  preparing  this  solution  is  described  under  Ethylene,  p.  249. 


252  GAS  ANALYSIS 

It  is  best  determined  by  leading  it  through  an  ammoniacal 
cuprous  chloride  solution,  a  reddish  brown  precipitate  being 
thrown  down.  The  precipitate  is  filtered  off,  and  is  washed  with 
water  containing  ammonia  until  the  wash-water  passes  through 
colorless.  The  moist  copper  acetylide  may  be  collected  in  a 
Gooch  crucible  and  dried  over  calcium  chloride  at  100°  in  a  cur- 
rent of  carbon  dioxide  :  and  weighed  as  Cu2C2.  Dry  copper 
acetylide  may,  however,  explode  at  a  temperature  as  low  as 
60°. 

The  acetylene  may  be  determined,  without  danger  of  explo- 
sion, by  taking  advantage  of  the  fact  that  the  moist  precipitate 
contains  carbon  and  copper2  in  the  atomic  proportion  of  1:1, 
and  determining  the  copper  in  the  moist  compound.  This 
is  done  by  pouring  hydrochloric  acid  upon  the  precipitate  which 
is  thereby  decomposed  with  evolution  of  acetylene.  As  it  is 
difficult  to  completely  decompose  the  copper  acetylide,  the  end 
of  the  reaction  is  not  waited  for,  but  the  rest  of  the  precipitate, 
without  being  washed,  is  dried  on  the  filter  and  ignited.  The 
copper  oxide  is  dissolved  in  a  few  drops  of  nitric  acid,  and  this 
solution  is  added  to  the  hydrochloric  acid  filtrate  first  obtained. 
The  copper  in  the  solution  may  then  be  determined  electrolyti- 
cally,  or  it  may  be  precipitated  from  hot  solution  with  sodium 
hydroxide,  filtered  off,  washed,  ignited  and  weighed  as  cupric 
oxide. 

Acetylene  may  be  determined  volumetrically  in  the  Hempel 
apparatus  by  absorbing  it  with  fuming  sulphuric  acid  contained 
in  the  pipette  shown  in  Fig.  86.  It  is  necessary  to  pass  the  gas 
repeatedly  into  the  pipette  until  no  further  diminution  in  vol- 
ume is  noted  upon  measuring  the  residual  gas  in  the  burette. 
Before  making  the  final  measurement,  the  gas  must,  of  course, 
be  passed  into  the  potassium  hydroxide  pipette  to  remove 
the  sulphur  trioxide.  Traces  of  acetylene  may  still  remain 
in  the  gas  mixture  after  this  treatment  with  fuming  sul- 

1  Scheiber,  Z.  analyt.  Chem.,  48  (1909),  537. 

2  Scheiber,  Ber.  d.  deutsch.  Chem.,  Ges.  41  (1908),  3816. 


PROPERTIES   OF  THE   VARIOUS   GASES  253 

phuric  acid,  and  these  may  be  removed  by  passing  the  gas  into 
a  pipette  containing  an  ammoniacal  cuprous  chloride  solution. 
If  oxygen  is  present  with  the  acetylene,  it  is  removed,  after  the 
treatment  of  a  gas  mixture  with  fuming  sulphuric  acid,  by  ab- 
sorption with  alkaline  pyrogallol.  Phosphorus  cannot  be  used 
for  the  absorption  of  oxygen  in  the  presence  of  even  very  small 
amounts  of  acetylene  because  the  gas  inhibits  the  union  between 
oxygen  and  phosphorus  to  such  an  extent  as  to  render  it  impos- 
sible to  obtain  even  approximately  correct  results  for  oxygen  with 
this  reagent. 

BENZENE   (C6H6) 

Specific  gravity  at  15°,  0.885.  Melting-point,  about  6°. 
Boiling-point,  80.3°. 

Determination  of  Benzene.  —  Benzene  is  rapidly  absorbed 
by  fuming  sulphuric  acid  and  this  reagent  may  be  employed  for 
the  determination  of  the  gas  if  no  other  heavy  hydrocarbons 
are  present.  This,  however,  is  rarely  the  case,  and  the  impor- 
tance of  benzene  as  an  illuminant  renders  very  desirable  the 
perfection  of  a  method  for  the  accurate  volumetric  separation 
and  determination  of  benzene  vapor  in  the  presence  of  other  of 
the  heavy  hydrocarbons. 

Absorption  of  Benzene  by  Alcohol.  —  In  1891  Hempel  and 
Dennis  1  proposed  a  method  for  the  removal  of  the  benzene 
vapor  that  was  based  on  the  ready  absorption  of  that  substance 
by  absolute  alcohol.  They  used  a  mercury  pipette  (Fig.  50) 
that  contained  above  the  mercury  i  cc.  of  absolute  alcohol 
that  was  first  saturated  with  the  illuminating  gas  under  exami- 
nation. After  the  removal  of  the  benzene  the  residual  alcohol 
vapor  was  absorbed  by  passing  the  gas  residue  into  a  mercury 
pipette  containing  i  cc.  of  water. 

Further  examination  2  of  this  method  demonstrated,  however, 
that  the  removal  of  benzene  vapor  by  alcohol  is  not  complete 

1  Berichte  der  deutschen  chemischen  Gesellschaft,  24  (1891),  1162. 

2  Dennis  and  O'Neill,  Jour.  Am.  Chem.  Soc.,  25  (1903),  503. 


2$4  GAS  ANALYSIS 

and  that  furthermore  the  solubility  of  various  gases  in  alcohol l 
is  so  appreciable  that  errors  arising  from  this  cause  cannot 
be  entirely  eliminated  by  saturation  of  the  alcohol  with  these 
gases. 

Absorption  of  Benzene  by  Paraffin  Oil.  —  The  removal  of 
benzene  by  cooled  paraffin  oil  was  proposed  by  Muller.2  The  gas 
mixture  is  first  dried  by  passing  it  through  apparatus  containing 
calcium  chloride  and  is  then  slowly  passed  through  an  absorption 
apparatus  containing  liquid  paraffin  of  0.88  to  0.89  specific  grav- 
ity and  of  a  boiling-point  of  about  360°.  The  absorption  ap- 
paratus is  weighed  before  the  experiment,  is  cooled  during  the 
experiment  with  a  freezing  mixture  of  ice  and  salt,  and  after 
the  absorption  is  brought  to  room  temperature  and  again 
weighed.  The  amount  of  gas  that  is  passed  through  the  ab- 
sorbent is  measured  by  a  gas  meter  placed  after  the  absorption 
apparatus. 

Determination  of  Benzene  as  Dinitrobenzene.  —  Harbeck 
and  Lunge  3  devised  a  method  for  the  determination  of  benzene 
that  is  based  upon  the  fact  that  benzene,  when  present  in  a 
gas  mixture  in  relatively  small  amount,  is  quantitatively  con- 
verted into  dinitrobenzene  when  the  gases  are  passed  through  a 
suitable  absorption  apparatus  containing  a  mixture  of  equal 
weights  of  concentrated  sulphuric  acid  and  fuming  nitric  acid. 
The  dinitrobenzene,  which  is  difficultly  soluble  in  water  but 
easily  soluble  in  ether,  is  extracted  with  ether  and,  after  evapora- 
tion of  the  solvent,  is  weighed.  From  this  weight  the  amount 
of  benzene  in  the  gas  is  calculated.  The  method  is  quite  accu- 
rate, but  unfortunately  it  is  so  time-consuming  as  to  preclude 
its  use  in  routine  analysis. 

Pfeiffer  determines  4  the  dinitrobenzene  obtained  by  the  Har- 
beck and  Lunge  method  by  a  volumetric  procedure  based  upon 

1  See  Lunge,  Chemisch-technische  Untersuchungsmethoden,  2,  585. 

2  /./.  Gasbeleuchtung,  41  (1898),  433. 

3  Z.f.  anorg.  Chem.,  1 6  (1808),  41;  also  Chemisch-technische  Untersuchungsmethoden, 
2,  592. 

4  Chemiker-Zeitung,  28  (1904),  884. 


PROPERTIES  OF  THE  VARIOUS   GASES  255 

the  reaction  first  mentioned  by  Limpricht 1  in  which  the  dinitro- 
benzene  is  reduced  to  diamidobenzene  by  stannous  chloride  and 
the  excess  of  the  reducing  agent  is  determined  by  titration  with 
an  iodine  solution  of  known  strength.  The  reactions  involved 
are 

C6H4  (NO2)2  +  6  SnCl2  +  12  HC1  = 

C6H4  (NH2)2  +  6  SnCl4  +  4  H2O, 
SnCl2  +  2  I  +  2  HC1  =  SnQ4  +  2  HI. 

Separation  of  Benzene  from  Ethylene. —  In  the  method  of 
Haber  and  Oechelhauser  2  the  total  amount  of  the  heavy  hydro- 
carbons is  determined  by  means  of  fuming  sulphuric  acid  and 
the  ethylene  in  another  sample  is  determined  by  absorption  in 
bromine  water  of  known  strength  and  titration  of  the  residual 
free  bromine  with  sodium  thiosulphate.  Assuming  that  only 
benzene  and  ethylene  are  present  the  amount  of  benzene  is 
equal  to  the  difference  between  these  two  results. 

The  method  gives  fairly  accurate  results,  but  it  is  open  to  the 
objection  that,  for  benzene,  it  is  indirect  and  that  a  determina- 
tion takes  considerable  time. 

Absorption  of  Benzene  with  Nickel  Solution. —  Dennis  and 
O'Neill  3  developed  a  gas  volumetric  method  for  the  determina- 
tion of  benzene  that  is  based  upon  the  reaction  that  takes  place 
when  nickel  cyanide,  ammonia  and  benzene  are  brought  to- 
gether, the  compound  Ni(CN)2»NH3'C6H6  being  formed.4  The 
absorbent  for  benzene  was  first  prepared  by  dissolving  nickel 
nitrate  in  water  and  pouring  this  solution  into  ammonium  hy- 
droxide. The  resulting  solution  had  a  slight  odor  of  ammonia. 
The  reagent  was  placed  in  a  Hempel  simple  absorption  pipette, 
the  gas  mixture  was  run  into  the  pipette  and  the  gas  shaken  with 
the  reagent  for  three  minutes.  It  was  then  drawn  back  into  the 

1  Ber.  d.  deutsch.  chem.  Ges.,  u  (1878),  35. 

2  Jour.  f.  Gasbeleuchtung,  39  (1896),  799;  43  (1900),  347. 

3  J.  Am.  Chem.  Soc.,  25  (1903),  503. 

4  Hofmann  and  Kiispert,  Z. /.  anorg.  Chem.,  15  (1897),  204. 


256  GAS  ANALYSIS 

burette,  passed  into  a  pipette  containing  mercury  and  5  cc.  of  a 
5%  solution  of  sulphuric  acid  to  remove  ammonia,  after  which  it 
was  drawn  back  and  finally  measured.  The  results  obtained 
with  this  method  by  different  analysts  were,  however,  quite  dis- 
cordant. Some  chemists  found  the  method  to  be  very  accurate 
while  others  reported  it  to  be  far  from  satisfactory.  A  careful 
examination  of  the  statements  from  different  analysts  rendered 
it  probable  that  those  samples  of  illuminating  gas  with  which 
the  method  gave  good  results  contain  the  cyanogen  compounds 
necessary  to  the  formation  of  the  product  described  by  Hofmann 
and  Kiispert,  and  that  the  poor  results  on  other  samples  of 
illuminating  gas  might  be  due  to  the  absence  of  cyanogen  com- 
pounds in  the  gas.  Consequently  the  solution  of  ammonia 
nickel  nitrate  was  replaced  l  by  a  solution  of  ammonia  nickel 
cyanide.  This  reagent  was  found  to  rapidly  and  quantita- 
tively absorb  benzene  from  mixtures  of  benzene  vapor  with  air 
as  well  as  from  samples  of  illuminating  gas,  and  it  was  further 
demonstrated  that  ethylene  was  not  taken  up  by  the  solution. 
The  reagent  is  prepared  as  follows : 

To  50  grams  of  nickel  sulphate  (NiSO^y  H^O),  dissolved  in 
75  cc.  of  water,  is  added  25  grams  of  potassium  cyanide  dissolved 
in  40  cc.  of  water.  After  the  addition  of  125  cc.  of  ammonium 
hydroxide  (Sp.  Gr.  0.9)  the  mixture  is  shaken  until  the  nickel 
cyanide  has  completely  dissolved.  It  is  then  cooled  to  o°  C.  and 
allowed  to  stand  at  that  temperature  for  twenty  minutes.  The 
clear  liquid  is  decanted  from  the  crystals  of  potassium  sulphate 
that  have  separated,  and  is  treated  with  a  solution  prepared  by 
dissolving  18  grams  of  crystallized  citric  acid  in  10  cc.  of  water. 
After  the  mixture  has  stood  again  at  o°  for  ten  minutes,  the 
greenish  blue  supernatant  solution  is  decanted  and  is  introduced 
into  a  gas  pipette.  Two  drops  of  liquid  benzene  are  now  added 
to  the  reagent  and  the  pipette  is  shaken  until  the  benzene  has 
combined  with  the  reagent,  which  is  evidenced  by  the  appear- 
ance of  a  fine,  granular,  white  precipitate  in  the  pipette.  This  is 

1  Dennis  and  McCarthy,  Jour.  Am.  Chem.  Soc.,  30  (1908),  233. 


PROPERTIES  OF  THE  VARIOUS   GASES  257 

effected  in  two  or  three  minutes.  This  addition  of  benzene  to 
the  reagent  is  made  because  it  has  been  found  that  a  freshly 
prepared  solution  of  the  ammonia  nickel  cyanide  does  not 
actively  remove  benzene  vapor  until  some  of  the  compound  be- 
tween benzene  and  the  reagent  has  been  formed. 

The  reagent  is  placed  in  a  Hempel  double  gas  pipette  for 
solid  reagents  (Fig.  37)  the  large  bulb  of  the  pipette  being 
filled  with  broken  glass.  The  absorbent  is  brought  into  the  first 
two  bulbs,  and  water  is  introduced  into  the  third  and  fourth 
bulbs.  The  analytical  absorbing  power  of  the  reagent  is  5 ;  con- 
sequently 100  cc.  of  the  reagent  in  the  pipette  may  be  used  in 
analytical  work  for  the  absorption  of  500  cc.  of  benzene  vapor. 

In  determining  benzene  by  this  method  a  gas  sample  is 
measured  off  in  a  gas  burette  which  is  then  connected  by  means 
of  the  usual  capillary  tube  with  the  pipette  containing  the  am- 
monia nickel  cyanide  solution.  The  gas  mixture  is  repeatedly 
passed  over  into  the  pipette  and  drawn  back  into  the  burette 
during  a  period  of  about  three  minutes,  which  will  suffice  for  the 
removal  of  the  benzene  in  amounts  up  to  about  eight  per  cent. 
The  gas  is  finally  drawn  into  the  burette  which  is  then  joined  to 
a  double  pipette  of  the  form  shown  in  Fig.  37.  The  bulb  A  is 
filled  with  glass  tubes  and  A  and  B  are  then  charged  with  a 
five  per  cent  solution  of  sulphuric  acid.  Bulbs  C  and  D  are 
filled  with  sufficient  water  to  protect  the  reagent  from  the  air. 
The  gas  residue  is  now  passed  back  and  forth  about  two  minutes 
to  remove  the  ammonia  that  enters  the.  gas  mixture  from  the 
reagent.  If  mercury  is  used  as  the  confining  liquid  in  the  burette 
the  small  amount  of  water  that  usually  covers  its  surface  will 
absorb  ammonia  from  the  reagent.  This  may  rapidly  be  re- 
moved by  drawing  into  the  burette  from  the  pipette  sufficient 
dilute  sulphuric  acid  to  completely  neutralize  the  ammonium 
hydroxide  thus  formed  and  then  driving  the  acid  back  into  the 
burette. 

Both  reagents  must  of  course  first  be  shaken  with  samples  of 
the  gas  mixture  under  analysis  in  order  to  saturate  the  absorb- 


258  GAS  ANALYSIS 

ents  with  those  constituents  of  the  mixture  which  they  do  not 
absorb. 

The  majority  of  those  who  have  used  this  method  in  technical 
practice  have  found  that  it  gives  uniform  and  accurate  results.1 

On  the  other  hand,  some  report  that  even  in  its  modified  form 
the  method  is  not  satisfactory.  In  the  greater  number  of  such 
cases,  correspondence  with  the  analyst  has  developed  either  that 
the  reagent  was  not  properly  prepared  or  that  the  absorption 
apparatus  was  of  an  inefficient  type.  But  little  weight  can  be 
attached  to  the  criticism  of  the  method  by  Harding  and  Taylor  2 
because  of  the  unconvincing  character  of  the  experimental 
work  of  those  authors.  They  compared  the  results  by  the 
ammonia  nickel  cyanide  method  with  those  obtained  by  another 
method  of  dubious  accuracy,3  using  a  gas  mixture  of  unknown 
benzene  content,  and  they  assume  that  differences  in  the  results 
are  due  to  the  inaccuracy  of  the  first  named  method.  They 
further  found  that  prolonged  contact  between  the  gas  mixture 
and  the  ammonia  nickel  cyanide  and  dilute  sulphuric  acid  caused 
a  slow  but  steady  diminution  of  the  gas  volume  and  they  as- 
cribed this  to  the  absorption  by  the  reagent  of  hydrocarbons 
other  than  benzene. 

To  test  the  correctness  of  this  assumption  and  to  ascertain 
whether,  as  Harding  and  Taylor  maintain,  there  is  slow  but 
continuous  absorption  of  gas  upon  repeated  passage  of  the  resi- 
due into  ammonia  nickel  cyanide  and  5  per  cent  sulphuric 
acid,  the  following  experiments  were  carried  out  in  the  author's 
laboratory  by  Mr.  E.  L.  Davies.  Mr.  Davies  placed  the  solu- 
tion of  ammonia  nickel  cyanide  and  of  5  per  cent  sulphuric 
acid  in  the  double  Hempel  pipettes  above  mentioned  and  passed 
into  these  pipettes  samples  of  the  city  gas  of  Ithaca,  which  is  a 
mixture  of  coal  gas  and  carburetted  water  gas.  Carbon  dioxide 

1  See,  for  example,  Pfeiffer,  Z.f.  angew.  Chem.,  20  (1907),  22;  Stavorinus,  Het  Gas, 
1905,  p.  554;  /./.  Gasbeleuchtung,  49  (1906),  272. 

2  Jour.  Ind.  and  Eng.  Chem.,  2  (1910),  345. 

3  See  Haber,  Jour.f.  Gasbeleuchtung,  43  (1900),  511. 


PROPERTIES  OF  THE  VARIOUS   GASES 


259 


was  of  course  first  removed  from  the  gas  by  means  of  potassium 
hydroxide.    He  obtained  the  results  that  are  tabulated  below. 


May  27, 

IQI2 

May  28, 

IQI2 

May  29, 

IQI2 

Volume  of  residue  after  removal  COz    . 
Volume   after  3   minutes   treatment  with 
nickel  solution  and  7  minutes  treatment 
with  5%  H2SO4 

96.8  cc. 

Q2      6    CC. 

97.0  cc. 

04.  .  2  CC. 

96.8  cc. 

04.        CC. 

Volume  after  first  repetition  with  these  two 
reagents        .      .            
Volume  after  26.  repetition    
"    id 

93  .  6  cc. 
93.6cc. 

01    ^  CC. 

94.2  cc. 
94.2  cc. 

04  .  2  CC. 

94      cc. 
94      cc. 
94       CC. 

"          "    4th       "                       .      .      . 

Ql  .  ^  CC. 

94  .  2  CC. 

94        CC. 

"    5th       "            
"    6th       " 

94  .  2  cc. 
94  .  2  cc. 

94      cc. 
94.1  cc. 

Total  duration  of  contact  with  nickel  solu- 
tion 

1  8  min. 

24  min. 

18  min. 

Total  duration  of  contact  with  5%  H2SO4 
Total  duration  of  contact  with  both  re- 
agents      

42  min. 
60  min. 

56  min. 
80  min. 

42  min. 
60  min. 

The  above  analyses  appear  to  demonstrate  conclusively  that 
the  solutions  of  ammonia  nickel  cyanide  and  5  per  cent  sul- 
phuric acid  do  not  gradually  absorb  constituents  of  the  gas 
mixture  other  than  benzene. 

The  results  of  the  experiments  with  ethylene  described  by 
Harding  and  Taylor  are  directly  contradictory  to  those  cited  by 
Dennis  and  McCarthy  and  are  probably  incorrect  both  because 
of  impurities  in  the  ethylene  that  was  used  and  because  of  solu- 
tion and  escape  of  the  gas  through  the  single  outer  bulb.  That 
they  find  that  a  gas  mixture  containing  ethylene  diminishes  in 
volume  when  shaken  with  ammonia  nickel  cyanide  for  even  so 
short  a  time  as  one  or  two  minutes  is  but  natural,  because  in  this 
as  in  all  other  cases  in  gas  analysis  a  liquid  reagent  will  dissolve 
somewhat  of  a  gas  and  must  be  saturated  with  the  gas  before  the 
analysis  is  made.1  That  acetylene  dissolves  both  in  the  reagent 
1  See  Dennis  and  McCarthy,  loc.  cit.,  p.  238. 


260  GAS  ANALYSIS 

and  in  the  5%  sulphuric  acid  is  not  at  all  surprising  because  that 
gas  is  quite  soluble  even  in  distilled  water.  The  point  is  quite 
beside  the  question  in  the  present  case  because  acetylene  does 
not  occur  as  a  constituent  of  ordinary  illuminating  gas. 

Stavorinus  J  subjected  the  method  to  a  careful  experimental 
examination  and  found  that  the  reagent  did  not  absorb  air, 
hydrogen,  carbon  monoxide,  methane,  pentane,  ethylene,  or 
propylene.  He  continues,  "Acetylene  on  the  other  hand  was 
absorbed,  which  was  to  be  expected,  but  since  this  gas  is  present 
in  illuminating  gas  in  scarcely  detectable  traces  it  may  be  dis- 
regarded. .  .  .  Gases  carburetted  with  benzene  gave  excel- 
lently agreeing  results,  and  the  method  can  furthermore  be 
commended  because  of  its  simplicity  of  manipulation,  and  its 
speed." 

NAPHTHALENE  (CioHg) 

Melting-point,  79°;  boiling-point,  218°. 

Naphthalene  is  a  white  crystalline  substance  that  is  solid  at 
ordinary  temperatures.  It  is,  however,  quite  volatile  and  for 
that  reason  its  vapor  is  frequently  present  in  carburetted  gas. 

Determination  of  Naphthalene.  —  For  the  determination  of 
naphthalene  in  gas  mixtures  the  method  original  with  Colman 
and  Smith,2  and  modified  and  improved  by  Gair,3  Rutten,4  Col- 
man,5  Jorissen  and  Rutten,6  and  Albrecht  and  Miiller  7  is  almost 
exclusively  employed.  It  is  based  upon  the  fact,  first  noted  by 
Fritzche,8  that  naphthalene  unites  with  picric  acid  to  form  a 
crystalline  compound  of  the  formula  CioHs'CeHsNaOr,  which  is 
but  slightly  soluble  in  a  saturated  or  nearly  saturated  solution 

1  Loc.  cit. 

2  Jour.  Soc.  Chem.  Ind.,  19  (1900),  128. 

3  Jour.  Soc.  Chem.  Ind.,  24  (1905),  1279. 

4  Eel  Gas,  1908,  Nos.  9  and  12. 

5  Jour.  Soc.  Chem.  Ind.,  28  (1909),  1179. 

6  Jour.  f.  Gasbeleuchtung,  53  (1910),  269. 
7Jour.f.Gasbeleuchtung,  54  (1911),  592. 
8  Jour,  prakt.  Chem.,  73  (1858),  282. 


PROPERTIES  OF  THE  VARIOUS   GASES  261 

of  picric  acid.    After  absorption  of  the  naphthalene,  the  excess 

N 

of  free  picric  acid  is  titrated  with  —  potassium  hydroxide. 

The  determination  may  be  carried  out  as  follows:  — 

The  gas  mixture,  which  must  be  free  from  tar,  cyanogen, 
hydrogen  sulphide  and  ammonia,1  is  passed  through  two  gas 
washing  bottles  containing  a  saturated  solution  of  picric  acid 
together  with  some  undissolved  picric  acid.  This  absorbing 
solution  is  prepared  by  weighing  off  exactly  2.5  grams  of  picric 
acid,  dividing  this  amount  of  the  acid  into  two  nearly  equal 
portions,  placing  one  portion  in  a  gas  washing  bottle  of  100  cc. 
capacity,  adding  25  cc.  of  water  and  then  shaking  the  bottle 
vigorously  until  a  saturated  solution  of  picric  acid  is  formed. 
The  other  portion  of  the  solid  picric  acid  is  then  placed  in  a 
second  gas  washing  bottle  and  treated  in  similar  manner.  The 
two  bottles  are  then  connected  to  each  other  glass  to  glass  by 
rubber  tubing,  and  the  gas  mixture -is  led  through  the  absorbent 
at  a  rate  of  from  40  to  50  liters  per  hour.  The  total  volume  of 
gas  passed  through  the  picric  acid  is  measured  by  a  gas  meter 
placed  after  the  wash  bottles  and  it  should  be  such  as  will 
contain  not  less  than  0.05  gram  and  not  more  than  0.20  gram  of 
naphthalene.2 

The  contents  of  the  two  wash  bottles  including  the  undis- 
solved picric  acid  is  carefully  transferred  to  a  250  cc.  measuring 
flask,  the  wash  bottles  being  rinsed  with  water.  The  stopper  of 
the  flask  is  inserted,  and  the  flask  is  then  heated  on  a  water  bath 
for  half  an  hour,  with  frequent  shaking,  to  from  40°  to  50°. 
This  will  cause  the  complete  solution  of  all  of  the  picric  acid. 

In  the  meantime  2.5  grams  of  picric  acid  is  weighed  out  into 
another  250  cc.  measuring  flask,  is  dissolved  in  water  and  is 
diluted  to  the  mark;  200  cc.  of  this  solution  is  then  titrated 

with  —  potassium  hydroxide,  lacmoid  being  used  as  indicator. 

1  See  analysis  of  illuminating  gas,  p.  306. 

2  Albrecht  and  Miiller,  loc.  cit. 


262  GAS  ANALYSIS 

The  measuring  flask  that  contains  the  picric  acid  by  which  the 
naphthalene  has  been  absorbed  is  allowed  to  cool  to  the  temper- 
ature of  the  room  and  is  then  filled  to  the  mark  with  water,  the 
contents  thoroughly  shaken,  and  200  cc.  of  the  solution  is  filtered 
off  through  a  dry  filter.  This  filtrate  is  then  also  titrated  with 

—  potassium  hydroxide.    The  difference  in  the  number  of  cubic 

centimeters  of  potassium  hydroxide  used  in  the  two  titrations 
multiplied  by  f-  X  0.0128  gives  the  grams  of  naphthalene  ab- 
sorbed by  the  picric  acid  in  the  two  wash  bottles.  This  amount 
is  then  calculated  to  grams  of  naphthalene  per  cubic  meter  of  gas. 

CYANOGEN    (C2N2) 

Properties  of  Cyanogen.  —  Specific  gravity,  1.7993;  weight 
of  one  liter,  2.3261  grams. 

One  volume  of  water  dissolves  at  20°,  4.5  volumes  of  cyanogen; 
i  volume  of  alcohol,  20  volumes  of  cyanogen. 

Burned  with  twice  its  volume  of  oxygen  it  forms  2  volumes  of 
carbon  dioxide  and  i  volume  of  nitrogen. 

Detection  of  Cyanogen.  —  Free  cyanogen,  or  dicyanogen, 
may  be  detected  according  to  Kunz-Krause  1  by  the  Schonbein- 
Pagenstecher  reaction.  For  carrying  out  this  test,  strips  of 
filter  paper  are  first  dipped  into  a  dilute  aqueous  solution  of 
copper  sulphate  (1:1000),  and  are  then  impregnated  with  a 
3  per  cent  tincture  of  gum  guaiac.  The  paper  thus  prepared 
turns  blue  when  acted  upon  by  dicyanogen  or  hydrocyanic  acid, 
but  this  blue  color  is  also  caused  by  certain  oxidizing  agents 
such  as  ozone  and  nitric  acid. 

The  reaction  is  somewhat  sharper  when  the  gas  mixture, 
instead  of  being  brought  in  contact  with  the  paper  above 
described,  is  passed  through  a  wash  bottle  containing  an  alcoholic 
copper  sulphate  —  gum  guaiac  solution. 

The  reaction  has  lately  been  increased  in  delicacy  by  E. 
Schaer,  who  uses  guaiaconic  acid  in  place  of  the  gum  guaiac. 

1  Zeitschr.  angew.  Chem.,  26  (1901),  652. 


PROPERTIES  OF  THE  VARIOUS   GASES  263 

The  reagent  should  always  be  freshly  prepared,  and  this  is  done 
by  adding  to  10  cc.  of  a  dilute  aqueous  copper  sulphate  solution 
15  cc.  of  alcohol  in  which  a  little  guaiaconic  acid  has  previously 
been  dissolved. 

Brimnich  states  1  that  the  delicacy  of  the  Schonbein-Pagen- 
stecher  test  for  hydrogen  cyanide  may  be  greatly  enhanced  by 
moistening  the  paper  with  formalin  instead  of  with  water  before 
exposing  the  paper  to  the  gas  mixture  under  examination.  The 
color  that  here  results  if  hydrogen  cyanide  is  present  is  deep 
blue,  whereas,  if  the  paper  is  moistened  with  water,  it  is  a  light 
blue. 

Another  delicate  reaction  for  dicyanogen  is  given  by  Kunz- 
Krause  in  the  article  above  cited,  this  test  depending  upon  the 
formation  of  isopurpuric  acid  or  picrocyaminic  acid,  C8H5N5O6, 
from  picric  acid.  2  cc.  of  a  cold  saturated  aqueous  solution  of 
picric  acid  (i:  86)  is  mixed  with  18  cc.  of  alcohol  and  5  cc.  of  a 
15  per  cent  aqueous  solution  of  potassium  hydroxide.  When 
brought  into  contact  with  this  solution  pure  cyanogen  yields  a 
deep  purple-red  color,  which  later  turns  to  brown.  On  long 
standing  the  potassium  salt  of  isopurpuric  acid  separates  in  the 
form  of  an  oil  of  purple-red  color.  This  reagent  also  must  always 
be  freshly  prepared. 

Potassium  hydroxide  absorbs  cyanogen,  potassium  cyanide 
and  potassium  cyanate  being  formed. 

C2N2  +  2  KOH  =  KCN  +  KCNO  +  H20. 

Determination  of  Cyanogen. —  Cyanogen  may  be  determined 
by  the  method  of  Nauss.2  100  liters  of  the  gas  mixture  is  passed 
at  a  rate  of  from  50  to  100  liters  per  hour  through  two  absorp- 
tion bottles  in  each  of  which  is  placed  20  cc.  of  a  solution  of 
ferrous  sulphate  (1:10)  and  20  cc.  of  a  solution  of  potassium 
hydroxide  (1:3).  After  the  passage  of  the  gas,  the  contents  of 
the  absorption  bottles  is  carefully  rinsed  into  a  500  cc.  flask, 

1  Chemical  News,  87  (1903),  173. 

2  J.  Gasbeleitchtung,  43  (1900),  696. 


264  GAS  ANALYSIS 

some  potassium  hydroxide  in  solution  is  added  and  then  ferrous 
sulphate  (1:10).  If  hydrogen  sulphide  is  present,  the  solution 
of  ferrous  sulphate  should  be  added  until  no  further  precipita- 
tion of  black  ferrous  sulphide  results.  It  is  advisable  to  add 
also  about  one  gram  of  lead  carbonate  to  ensure  the  complete 
removal  of  hydrogen  sulphide.  The  contents  of  the  flask  is  then 
heated  for  some  minutes  and  allowed  to  cool.  The  flask  is  filled 
to  the  mark,  and  5  cc.  more  of  water  is  added  to  compensate  for 
the  volume  of  the  precipitate.  After  being  vigorously  shaken, 
the  liquid  is  filtered  off  through  a  dry  paper;  50  cc.  of  the 
filtrate  is  poured  into  an  excess  (20  to  30  cc.)  of  a  hot  solution  of 
ferric  alum  that  contains  200  grams  of  ferric  alum  to  the  liter. 
The  solution  is  warmed  for  a  short  time  on  a  water  bath  and 
Prussian  blue  is  then  precipitated  by  the  addition  of  dilute 
sulphuric  acid.  The  precipitate  is  collected  on  a  folded  filter  in 
a  hot-water  funnel,  and  is  washed  with  hot  water  until  sulphuric 
acid  has  been  completely  removed.  The  precipitate  with  the 
filter  is  then  at  once  placed  in  a  flask,  some  water  is  added,  and 
the  liquid  is  heated  to  boiling,  the  contents  of  the  flask  being 
frequently  shaken  to  loosen  the  precipitate  from  the  paper.  The 
amount  of  the  Prussian  blue  is  then  directly  determined  by 
titration  with  a  -^N  solution  of  sodium  hydroxide. 

Fe4(Fe(CN)6)3  +  12  NaOH  =  4  Fe(OH)3  +  3  Na4  Fe(CN)6. 

The  solution  of  sodium  hydroxide  is  added,  a  little  at  a  time, 
until  all  of  the  Prussian  blue  is  decomposed.  The  contents  of 
the  flask  is  kept  hot  during  the  addition  of  the  sodium  hydroxide 
for  the  purpose  of  hastening  the  reaction.  The  excess  of  sodium 
hydroxide  is  then  ascertained  by  titrating  back  with  -^N  acid. 
The  liquid  must  be  continuously  heated  and  frequently  shaken 
during  this  last  titration,  for  even  in  the  presence  of  an  excess  of 
sodium  hydroxide  there  is  some  re-formation  of  Prussian  blue 
which  causes  a  green  coloration  of  the  liquid.  When  the  color 
changes  to  a  light  greenish  yellow,  the  end  point  has  been  reached. 

i  cc.  -jpj-N  sodium  hydroxide  =  0.0007794  gram  cyanogen. 


PROPERTIES  OF  THE  VARIOUS   GASES  265 

Nauss  found  from  6  to  15  grams  of  cyanogen  in  100  cubic 
meters  of  Karlsruhe  gas  after  the  last  purifier. 

Samtleben,  using  the  analytical  method  of  Nauss,  found  *  in 
coal  gas  of  Bernburg  from  155  to  301  grams  of  hydrogen  cyanide 
in  100  cubic  meters  before  the  purifiers,  and  from  8.8  to  21.3 
grams  per  100  cubic  meters  after  the  purifiers. 

Detection  and  Determination  of  Cyanogen  in  presence  of 
Hydrogen  Cyanide.  —  Wallis  2  observed  that  when  hydrogen 
cyanide  is  passed  into  an  acidified  solution  of  silver  nitrate  it  re- 
acts quantitatively  with  the  silver  nitrate  to  precipitate  silver 
cyanide.  He  also  states  that  cyanogen  does  not  react  with  an 
acidified  solution  of  silver  nitrate,  and  that  any  cyanogen  that 
dissolves  as  such  in  the  reagent  may  be  removed  practically  com- 
pletely by  passing  a  current  of  air  through  the  solution.  Upon 
this  difference  of  behavior  of  cyanogen  and  hydrogen  cyanide 
toward  silver  nitrate,  Wallis  bases  a  method  for  the  detection 
of  cyanogen  and  of  hydrogen  cyanide  when  these  gases  are 
present  together  in  a  gas  mixture,  but  he  carried  the  work  no 
further  than  to  show  the  applicability  of  this  method  to  the 
qualitative  examination  of  a  few  special  gas  mixtures. 

Quite  recently  Rhodes  has  made  a  careful  study  of  the  re- 
action noted  by  Wallis  and  has  developed  a  method  3  that 
permits  both  of  the  detection  and  of  the  accurate  determina- 
tion of  cyanogen  in  the  presence  of  hydrogen  cyanide.  For 
the  detection  of  cyanogen  in  the  presence  of  hydrogen  cyanide 
he  proceeds  as  follows  — 

Test  tubes  15  cm.  long  and  provided  with  side  arms  are  used 
for  the  absorption  of  the  gases.  In  one  such  tube  is  placed  10  cc. 
of  a  10  per  cent  solution  of  silver  nitrate  to  which  one  drop  of 
dilute  (6  N)  nitric  acid  has  been  added.  In  the  second  tube  is 
placed  10  cc.  of  a  2  N  solution  of  potassium  hydroxide.  The  two 
absorption  tubes  are  connected  in  series  and  the  gas  mixture  is 

1  /.  Gasbeleuchtung,  49  (1906),  205. 

2  Annalen  (Liebig)  345  (1906),  353. 

3  J.  Ind.  and  Eng.  Chem.,  4  (1912),  652. 


266  GAS  ANALYSIS 

passed  through  them.  The  duration  of  the  passage  of  the  gas 
depends  upon  the  amount  of  hydrogen  cyanide  in  the  gas  mix- 
ture. Since  the  first  tube  is  intended  to  hold  back  the  hydrogen 
cyanide,  the  passage  of  the  gas  must  of  course  be  stopped  before 
all  of  the  silver  nitrate  in  this  tube  is  converted  into  silver  cy- 
anide. After  the  gas  mixture  has  been  passed  through  the  ab- 
sorption tubes  for  a  sufficient  length  of  time,  it  is  replaced  by  a 
current  of  air  which  is  continued  for  about  ten  minutes.  The 
second  absorption  tube,  which  contains  the  solution  of  potas- 
sium hydroxide,  is  then  disconnected  and  5  cc.  of  a  solution  of 
ferrous  sulphate  and  one  drop  of  a  solution  of  ferric  chloride 
are  added  to  the  contents  of  the  tube.  After  about  fifteen  min- 
utes there  is  added  dilute  sulphuric  acid  in  amount  sufficient  to 
dissolve  the  ferrous  and  ferric  hydroxides.  The  appearance  of 
a  blue  precipitate  or  of  a  distinct  green  color  in  the  solution  after 
acidification  proves  the  presence  of  cyanogen  in  the  original 
gas  mixture.  The  delicacy  of  this  reaction  for  cyanogen  is 
shown  by  the  results  in  the  following  table :  — 

VOLUME  OF  CYANOGEN  COLOR  DEVELOPED 

10.     cc.  Blue  precipitate 

5 .    cc.  Blue  precipitate 

i .    cc.  Blue  precipitate 

0.4  cc.  Green  color 

0.3  cc.  Faint  green  color 

o .  2  cc.  Very  faint  green  color 

From  the  above  data  it  appears  that  as  small  an  amount  as 
0.3  cc.  of  cyanogen  may  be  detected  in  this  manner.  That  the 
presence  of  hydrogen  cyanide  in  the  gas  does  not  interfere  with 
the  delicacy  of  this  method  was  demonstrated  by  passing  through 
the  absorbents  a  mixture  of  0.4  cc.  of  cyanogen  and  10  cc.  of 
hydrogen  cyanide  and  obtaining  a  distinct  reaction  for  cyanogen 
under  these  conditions. 

Since  potassium  cyanide  is  hydrolyzed  to  a  considerable  degree 
in  aqueous  solution  with  the  formation  of  hydrocyanic  acid, 


PROPERTIES   OF  THE   VARIOUS   GASES  267 

it  was  thought  possible  that  the  passage  of  a  large  volume  of 
air  through  the  apparatus  might  carry  with  it  some  of  the  hydro- 
gen cyanide,  and  thus  decrease  the  delicacy  of  the  test.  It  was 
found,  however,  that  this  was  not  the  case,  0.4  cc.  of  cyanogen 
still  yielding  a  distinct  reaction  when  20  liters  of  air  was  passed 
through  the  apparatus  subsequent  to  the  introduction  of  the 
cyanogen. 

A  small  amount  of  carbon  dioxide  in  the  gas  mixture  under 
examination  does  not  interfere  with  the  test  for  cyanogen.  But 
if  an  amount  of  gas  containing  carbon  dioxide  sufficient  to  con- 
vert all  of  the  potassium  hydroxide  into  potassium  carbonate 
is  passed  through  the  reagent,  the  reaction  for  cyanogen  is  then 
not  obtained. 

The  presence  of  hydrogen  cyanide  in  the  original  gas  mixture 
is  detected  by  collecting  on  a  filter  any  precipitate  that  may 
have  formed  in  the  solution  of  silver  nitrate  in  the  first  absorp- 
tion tube,  washing  the  precipitate  with  very  dilute  nitric  acid, 
drying  it,  transferring  it  to  a  small  sublimation  tube,  and 
warming  it  with  a  small  amount,  five  milligrams  or  less,  of 
iodine.  The  formation  of  a  sublimate  of  cyanogen  iodide  on 
the  side  of  the  tube  proves  the  presence  of  silver  cyanide  in 
the  precipitate  and  consequently  of  hydrogen  cyanide  in  the 
original  gas  mixture;  o.i  mg.  of  silver  cyanide,  equivalent 
to  0.02  mg.  of  hydrogen  cyanide,  may  be  detected  in  this 
manner. 

To  determine  cyanogen  and  hydrogen  cyanide  in  the  presence 
of  each  other  the  gas  mixture  is  passed  through  a  series  of  four 
absorption  test  tubes.  Each  of  the  first  two  of  these  tubes  con- 
tains 5  cc.  of  a  standardized  (approximately  — )  solution  of 

silver  nitrate  and  one  drop  of  dilute  nitric  acid.  In  the  third 
absorption  tube  is  placed  10  cc.  of  an  approximately  2  N  solu- 
tion of  potassium  hydroxide  that  is  free  from  chloride,  and  the 
last  tube  contains  5  cc.  of  this  solution.  The  gas  mixture  under 
examination  is  slowly  passed  through  this  absorption  apparatus 


268  GAS  ANALYSIS 

or  is  carried  through  by  a  slow  current  of  air.  The  first  two 
absorption  tubes  are  then  disconnected  and  the  solution  of 
silver  nitrate  that  they  contain  is  transferred  to  a  beaker  and  is 
filtered.  The  precipitate  and  filter  paper  are  washed  with  very 
dilute  nitric  acid  until  free  from  soluble  silver  salts.  The  filtrate 
and  wash  water  are  then  combined  and  are  titrated  with  a  stand- 
ardized solution  of  ammonium  sulphocyanate  with  ammonium 
ferric  alum  as  indicator,  and  the  amount  of  hydrogen  cyanide 
that  was  present  in  the  original  gas  mixture  is  calculated  from 
the  volume  of  ammonium  sulphocyanate  used. 

The  contents  of  the  third  and  fourth  absorption  tubes  is 
transferred  to  a  beaker  and  a  known  volume  of  a  standardized 
solution  of  silver  nitrate  is  added.  The  silver  nitrate  must  be 
in  excess  of  the  amount  required  to  precipitate  all  of  the  potas- 
sium cyanide  in  the  solution  as  silver  cyanide.  The  solution 
and  the  suspended  precipitate,  are  then  thoroughly  stirred,  and 
dilute  nitric  acid  is  next  added  until  the  precipitated  silver  oxide 
redissolves  and  the  solution  becomes  slightly  acid.  The  pre- 
cipitate of  silver  cyanide  is  now  filtered  off,  the  precipitate  and 
filter  paper  are  washed  with  very  dilute  nitric  acid  until  all 
soluble  silver  salts  are  removed,  and  the  filtrate  and  wash  water 
are  combined  and  are  titrated  with  a  standardized  solution  of 
ammonium  sulphocyanate  with  ammonium  ferric  alum  as  in- 
dicator. The  cyanogen  present  in  the  original  gas  mixture  is 
then  calculated,  the  reactions  involved  in  the  calculation 
being:  — 

(CN)2     +  2  KOH     =  KCN      +  KCNO  +  H2O 
KCN      +     AgNO3  =  AgCN     +  KNO3 
AgNO3   +     KCNS    =  AgCNS  +  KNO3 

Analyses  made  by  this  method  of  mixtures  of  known  amounts 
of  cyanogen  and  hydrogen  cyanide  showed  that  the  procedure 
gives  very  satisfactory  results. 


PROPERTIES   OF  THE   VARIOUS   GASES  269 

HYDROGEN   CYANIDE    (HCN) 

Properties  of  Hydrogen  Cyanide. —  Specific  gravity,  0.9359; 
weight  of  one  liter,  1.2096  grams. 

The  gas  is  easily  soluble  in  water  and  in  alcohol,  and  is  ab- 
sorbed by  potassium  hydroxide  with  the  formation  of  potassium 
cyanide. 

Strong  acids,  especially  hydrochloric  acid  and  sulphuric  acid, 
decompose  hydrocyanic  acid  with  formation  of  formic  acid  and 
ammonia. 

Detection  of  Hydrogen  Cyanide.  —  Hydrogen  cyanide  may 
be  detected  by  absorbing  the  gas  in  a  solution  of  potassium  hy- 
droxide, and  then  adding  ferrous  sulphate  and  one  drop  of  fer- 
ric chloride  to  the  solution  of  potassium  cyanide.  (If  the  solu- 
tion that  is  being  tested  is  not  alkaline,  potassium  hydroxide 
should  be  added  at  this  point.)  The  solution  is  then  gently 
warmed  and  is  acidified  with  hydrochloric  acid.  A  dark  blue 
precipitate  of  Prussian  blue  proves  the  presence  of  potassium 
cyanide  in  the  absorbent.  Since  cyanogen  is  absorbed  by  potas- 
sium hydroxide  with  the  formation  of  potassium  cyanide,  that 
gas  will  also  give  this  reaction. 

Another  test  for  hydrocyanic  acid  is  to  add  ammonium  sul- 
phide until  the  solution  takes  on  a  yellow  color,  then  ammonia,  — 
or,  better,  a  drop  of  sodium  hydroxide,  —  and  to  heat  the  solu- 
tion until  the  excess  of  ammonium  sulphide  has  been  driven  off, 
and  the  solution  is  again  colorless.  In  this  way  there  is  formed 
either  ammonium  or  sodium  sulphocyanate,  which,  after  acidi- 
fying, gives  the  characteristic  blood-red  color  with  ferric  chloride. 

Hydrogen  cyanide  may  also  be  detected  by  the  methods  pro- 
posed by  Kunz-Krause  and  by  Schaer  which  have  already  been 
described  under  Cyanogen. 

Determination  of  Hydrogen  Cyanide. —  For  the  determina- 
tion of  hydrogen  cyanide  in  a  gas  mixture  the  method  of  L.  W. 
Andrews  1  may  be  used.  The  gas  is  absorbed  in  potassium  hy- 

1  American  Chemical  Journal,  30  (1903),  187. 


270  GAS  ANALYSIS 

dioxide  and  if  the  resulting  solution  contains  more  than  about 
one  per  cent  of  hydrogen  cyanide,  it  is  diluted  with  water  until 
its  concentration  does  not  exceed  one  per  cent.  Two  drops  of  a 
saturated  solution  of  pure  paranitrophenol  are  then  added.  If 
the  solution  takes  on  a  yellow  color,  decinormal  hydrochloric 
acid  is  added  until  the  color  has  very  nearly  disappeared.  On 
the  other  hand,  if  the  solution  remains  colorless,  a  decinormal 
solution  of  potassium  hydroxide  is  added  until  a  very  pale- 
yellow  tint  is  observed.  15  to  20  cc.  of  a  solution  of  mercuric 
chloride  containing  40  grams  of  the  pure  recrystallized  salt  to 
the  liter  is  then  added,  and  the  solution  is  stirred  and  is  allowed 
to  stand  for  one  hour  at  the  temperature  of  the  air.  The  hydro- 
chloric acid  set  free  in  the  reaction 

HgCl2  +  2  HCN  =  Hg  (CN)2  +  2  HC1 

is  then  titrated  with  a  decinormal  solution  of  potassium  hydrox- 
ide, the  end  point  of  the  titration  being  shown  by  the  appear- 
ance of  a  pale-yellow  tint  in  the  solution. 

HYDROGEN   SULPHIDE    (H2S) 

Properties   of   Hydrogen   Sulphide.  —  Specific    gravity, 
1.1773;  weight  of  one  liter,  1.5230  grams. 
According  to  Bunsen's  experiments,  water  absorbs:  — 

at    2°     C.,  4.2373  vol.  H2S 
"    9.8°  C.,  3.5446     "     " 
"  14.6°  C.,  3.2651     " 
"  19°     C.,  2.9050     " 

Between  2°  and  43.3°  the  absorption  by  one  volume  of  water  at  t° 
=  4.3706  —  0.083687  t  +  0.0005213  t2  volumes  of  H2S. 

According  to  the  same  authority  alcohol  takes  up,  between  i° 
and  22°,  at  temperature  /, 

17.891  —  0.65598  t  +  0.00661  t2  volumes. 


PROPERTIES  OF  THE  VARIOUS   GASES  271 

One  and  a  half  volumes  of  oxygen  are  necessary  for  the  com- 
bustion of  one  volume  of  hydrogen  sulphide,  and  one  volume  of 
sulphur  dioxide  is  formed. 

2  H2S  +  3  O2  =  2  H2O  +  2  SO2. 

Potassium  hydroxide  and  solutions  of  salts  of  several  other 
metals  absorb  hydrogen  sulphide  with  the  formation  of  a  sul- 
phide of  the  metals. 

Detection  of  Hydrogen  Sulphide.  —  If  hydrogen  sulphide  is 
present  in  any  considerable  amount,  its  presence  is  disclosed  by 
its  odor.  It  may  more  certainly  be  detected  by  introducing  into 
the  gas  a  strip  of  moistened  "  lead-paper."  Lead-paper  is  made 
by  dipping  filter  paper  into  a  solution  of  lead  acetate,  drying  it 
and  cutting  it  into  narrow  strips.  In  using  it  for  testing  for 
hydrogen  sulphide  it  should  first  be  moistened  either  with  water 
or  with  dilute  ammonium  hydroxide.  If  hydrogen  sulphide  is 
present  in  the  gas  mixture,  the  paper  becomes  covered  with  a 
glistening  brownish  black  layer  of  lead  sulphide. 

Another  method  for  the  detection  of  hydrogen  sulphide  is  that 
devised  by  Ganassini.1  It  is  based  upon  the  fact  that  when  am- 
monium molybdate  is  reduced  by  hydrogen  sulphide,  the  molyb- 
denum salt  will  react  with  potassium  sulphocyanate  to  form  mo- 
lybdenum sulphocyanate  which  when  dissolved  in  water  yields  a 
solution  of  pinkish  red  color.  The  reagent  is  prepared  by  dis- 
solving 1.25  grams  of  ammonium  molybdate  in  50  cc.  of  water 
and  2.5  grams  of  potassium  sulphocyanate  in  45  cc.  of  water,  mix- 
ing these  two  solutions  and  acidifying  with  5  cc.  of  concentrated 
hydrochloric  acid.  The  solution  is  said  to  be  stable  for  some  days 
if  kept  in  a  stoppered  bottle  and  protected  from  the  light.  To 
test  for  the  presence  of  hydrogen  sulphide  in  the  gas  mixture  the 
inside  of  a  small  porcelain  evaporator  is  moistened  with  the  re- 
agent, and  the  gas  under  examination  is  caused  to  impinge  upon 
the  moistened  surface.  The  test  may  also  be  made  by  dipping  a 
piece  of  filter  paper  into  the  reagent  and  holding  the  moistened 
1  Boll.  Chim.  Farm.,  41  (1902),  417. 


272  GAS  ANALYSIS 

paper  in  the  gas.  If  hydrogen  sulphide  is  present,  the  liquid  or 
the  paper  takes  on  a  color  that  varies  from  a  pale  pink  to  a  deep 
pinkish  red  according  to  the  amount  of  hydrogen  sulphide  in  the 
gas.  Neither  acetylene  nor  sulphur  dioxide  produces  the  red 
coloration. 

Determination  of  Hydrogen  Sulphide. — Hydrogen  sulphide 
may  quantitatively  be  determined  by  Dupasquier's  method,  a 
measured  quantity  of  gas  being  drawn  through  a  solution  of 
iodine  in  potassium  iodide,  to  which  some  starch  paste  has  been 
added.  The  operation  is  stopped  as  soon  as  the  solution  be- 
comes colorless.  The  reaction  is  — 

H2S  +  2  I  =  2  HI  +  S, 

but  the  reaction  follows  this  equation  precisely  only  when  the 
solutions  are  very  dilute  and  are  protected  from  direct  sun- 
light 

R.  Fresenius  1  determines  hydrogen  sulphide  gravimetrically 
by  first  drying  the  gases  with  calcium  chloride  and  then  absorb- 
ing the  hydrogen  sulphide  in  U-tubes  which  are  filled  §  with 
pumice-stone  impregnated  with  copper  sulphate,  and  ^,  at  the 
exit  end,  with  calcium  chloride.  The  pumice-stone  is  prepared 
as  follows:  Place  60  grams  of  pumice-stone,  in  pieces  the  size  of 
a  pea,  in  a  small  porcelain  dish,  and  pour  a  hot  concentrated 
solution  of  from  30  to  35  grams  of  copper  sulphate  over  it. 
Evaporate  the  solution  to  dry  ness  with  constant  stirring,  place 
the  dish  in  an  air-  or  oil-bath,  whose  temperature  is  kept  between 
150°  and  1 60°  C.,  and  let  it  remain  there  four  hours. 

A  tube  containing  14  grams  of  this  copper  sulphate  pumice- 
stone  takes  up  about  2  grams  of  hydrogen  sulphide.  To  make 
sure  of  complete  absorption  two  such  tubes  should  always  be 
used.  When  the  pumice-stone  is  less  thoroughly  dried,  it  takes 
up  a  much  smaller  amount  of  hydrogen  sulphide,  and  when  it 
has  been  dried  at  a  higher  heat  —  until  the  copper  sulphate  has 

1  R.  Fresenius,  Anleitung  zur  quant.  Analyse,  6th  ed.,  Part  I,  p.  505.  Also  Zeitschr. 
f.  analyt.  Chentie,  10  (1871),  75. 


PROPERTIES   OF  THE   VARIOUS   GASES  273 

lost  its  water  of  crystallization  —  it  causes  decomposition  of  the 
hydrogen  sulphide  and  evolution  of  sulphur  dioxide. 

SULPHUR  DIOXIDE    (SC^) 

Properties  of  Sulphur  Dioxide.  —  Specific  gravity,  2.2131; 
weight  of  one  liter,  2.8611  grams. 

Sulphur  dioxide  is  easily  soluble  in  water.  According  to  Sims, 
i  volume  of  water  dissolves  at  760  mm.  pressure  — 

at  7°,       61.65  vol.  SO2 
"  20°,     36.43    "      " 
"  39-8°,  20.5      "      " 
"  50°,     15.62    " 

One  volume  of  water  absorbs  at  760  mm.  pressure,  and  at  tem- 
peratures between  o°  and  20°,  at  /°, 

79.789  —  2.6077  ^  +  °-°29349  i2 

volumes  of  sulphur  dioxide;  and  i  volume  of  the  saturated 
aqueous  solution  contains,  at  /°, 

68.861  —  1.87025  /  +  0.01225  ^ 

volumes  of  the  acid. 

For  temperatures  between  21°  and  40°,  the  coefficient  of 
absorption  is  — 

75.182  —  2.1716  t  +  0.01903  t2, 

and  the  amount  of  gas  contained  by  the  saturated  aqueous 
solution  is  — 

60.952  —  1.38898  i  +  0.00726  /2  volumes. 

One  volume  of  alcohol  absorbs  at  760  mm.  pressure  and  t°, 
328.62  —  16.95  ^  +  °-3II9  P  volumes  of  sulphur  dioxide. 

The  alcoholic  solution  of  sulphur  dioxide,  saturated  at  o°, 
contains  216.4  volumes  of  the  gas. 

The  gas  reddens  moist  blue  litmus  paper. 


274  GAS  ANALYSIS 

The  gas  is  readily  absorbed  by  solutions  of  the  hydroxides  of 
the  alkali  metals. 

Determination  of  Sulphur  Dioxide.  —  Sulphur  dioxide  is 
determined  either  by  leading  a  measured  volume  of  the  gas 
through  a  solution  of  bromine  in  water,  and  precipitating  the 
sulphuric  acid  thus  formed  by  barium  chloride,  or  by  measuring 
the  amount  of  gas  required  to  decolorize  an  iodine  solution  of 
known  strength, 

SO2  +  2  I  +  2  H2O  =  H2SO4  +  2  HI. 

This  latter  method  is  very  generally  employed  for  the  de- 
termination of  sulphur  dioxide  in  "burner  gas,"  the  usual  pro- 
cedure being  that  recommended  by  Reich.1  The  operation  may 
be  carried  out  in  the  apparatus  shown  in  Fig.  25.  A  is  a  Fried- 
rich's  spiral  gas  washing  bottle,  B  is  a  glass  bottle  of  about  three 
liters  capacity  and  C  is  a  250  cc.  graduated  cylinder.  10  cc.  of  a 
standard  solution  of  iodine  containing  12.692  grams  of  iodine 
to  the  liter  is  poured  into  A.  65  cc.  of  water  is  then  added  to- 
gether with  sufficient  of  a  starch  solution  to  give  to  the  liquid 
an  intense  blue  color.  B  is  rilled  nearly  to  the  top  with  water 
and  the  siphon  tube  D  is  filled  with  water  by  applying  suction 
at  its  lower  end.  The  apparatus  is  then  connected  as  shown 
in  the  figure  and  the  inlet  tube  of  A  is  joined  by  glass  tubing 
to  the  chamber  or  pipe  from  which  the  gas  is  to  be  drawn.  The 
screw  pinchcock  E  is  now  opened  and  water  is  allowed  to  run 
out  of  B  until  a  gas  bubble  starts  to  rise  in  the  absorption  bot- 
tle A.  The  graduated  cylinder  is  then  placed  under  the  end  of 
D  and  the  water  that  flows  from  B  is  collected  in  it.  In  this 
manner  the  gas  is  slowly  aspirated  through  the  iodine  solution 
until  the  liquid  is  decolorized.  The  pinchcock  E  is  then  at  once 
closed  and  the  volume  of  water  that  has  collected  in  the  gradu- 
ated cylinder  is  measured. 

The  amount  of  sulphur  dioxide  in  the  mixture  under  examina- 

1  F.  Reich,  Berg-und  Huttenmdnn.  Zeitung,  1858. 


PROPERTIES   OF  THE  VARIOUS   GASES  275 

tion  may  then  be  calculated  as  follows:  One  cc.  of  the  standard 
iodine  solution  corresponds  to  0.0032  gram  SO2  which  amount 
under  standard  conditions  possesses  a  volume  of  1.118  cc.  If 
b  equals  the  prevailing  barometric  pressure,  /  the  temperature, 
h  the  difference  in  height  in  millimeters  between  the  level  of 
the  water  in  B  and  the  lower  end  of  the  siphon  tube  D,  and  n 
the  cubic  centimeters  of  iodine  solution  employed,  then  the  ac- 
tual volume  under  the  prevailing  conditions  of  the  sulphur 
dioxide,  s,  that  has  passed  through  the  iodine  solution  may  be 
calculated  by  use  of  the  following  formula: 

s  =  1.118  X  n  X  -  7—^—  X   (i  +  0.00367  t)  cc. 


The  volume  of  the  water,  w,  in  the  graduated  cylinder  C  is 
equal  to  the  amount  of  gas  that  has  been  drawn  through  A 
exclusive  of  the  volume  of  sulphur  dioxide;  consequently  the 
total  volume  of  gas  drawn  into  A  equals  w  -\-  s  and  the  per  cent 

of  sulphur  dioxide  in  the  gas  mixture  equals  - 

If  it  should  not  be  deemed  necessary  to  introduce  correc- 
tions for  the  pressure  and  temperature,  the  formula  becomes 

m.Sxn 

=  per  cent  862. 


w  +  1.118  x  n 

If  10  cubic  centimeters  of  the  standard  (decinormal)  iodine 
solution  is  used,  the  volume  percentage  of  sulphur  dioxide  in 
the  original  gas  mixture  that  is  indicated  by  different  volumes  of 
water  collected  in  the  graduated  cylinder  is  shown  in  the  table 
on  page  276. l 

An  apparatus  that  \$  based  upon  the  same  principle  as  that 
of  Reich,  but  which  is  so  constructed  that  the  per  cent  of  sul- 
1  Lunge,  Sulphuric  and  Alkali,  1903,  vol.  i,  part  i,  p.  415. 


276  GAS  ANALYSIS 

CUBIC  CENTIMETERS  WATER  VOLUME  PER  CENT  SO  2 

COLLECTED  IN  KILN  GAS 

82  12 

86  II. 5 

90  II 

95  io-5 

ICO  10 

106  9.5 

US  9 

i 20  8.5 

128  8 

138  7-5 

148  7 

i 60  6.5 

175  6 

192  5-5 

212  5 

phur  dioxide  in  the  gas  mixture  may  be  directly  read  off,  has 
been  described  by  Kreidl.1 

Determination  of  Sulphur  Dioxide  in  presence  of  Nitrous 
Acid.  —  The  method  of  Reich  cannot  be  used  for  the  determina- 
tion of  sulphur  dioxide  in  the  gases  from  the  lead  chambers  of  the 
sulphuric  acid  process  because  the  hydriodic  acid  that  is  formed 
is  quickly  oxidized  again  to  iodine  by  the  nitrous  acid  that  is 
present.  The  iodine  that  is  thus  set  free  then  oxidizes  additional 
amounts  of  sulphur  dioxide  with  the  result  that  the  percentage 
of  sulphur  dioxide  in  the  gas  mixture  appears  to  be  much  smaller 
than  it  actually  is.  Moreover,  the  presence  of  nitrous  acid  ren- 
ders the  end  point  of  the  reaction,  the  decolorization  of  the  iodine 
solution,  uncertain  for  the  reason  that  after  decolorization  has 
been  effected  by  the  sulphur  dioxide  the  blue  color  reappears 
because  of  the  action  of  the  nitrous  acid.  For  the  determination 
of  sulphur  dioxide  in  the  presence  of  nitrous  acid,  it  is  conse- 
quently necessary  to  modify  the  method  in  such  manner  as  to 
prevent  the  interference  of  nitrous  acid  and  this  is  accomplished 
by  Raschig  2  by  adding  sodium  acetate  to  the  solution.  This 

1  Z.f.  Zuck,-Ind.  Bohm.,  24  (1900),  658. 

2  Z./.  angewandte  Chern.,  22  (1909),  1182. 


PROPERTIES  OF  THE  VARIOUS   GASES  277 

reacts  with  the  free  nitrous  acid  to  form  sodium  nitrite  and  with 
the  sulphur  dioxide  to  form  sodium  sulphite,  and  these  two  salts 
do  not  act  upon  each  other. 

In  the  Raschig  method  the  absorption  bottle  A}  Fig.  25, 
contains  10  cc.  of  decinormal  iodine  solution,  about  60  cc.  of 
water,  a  little  starch  solution  and  10  cc.  of  a  cold  saturated  solu- 
tion of  sodium  acetate.  A  U-tube  or  bulb  tube  containing 
cotton  is  placed  between  A  and  the  lead  chambers  to  prevent 
sulphuric  acid  from  passing  into  the  iodine  solution.  The  amount 
of  sulphur  dioxide  in  the  gas  mixture  is  determined  in  the  manner 
already  described  under  the  Reich  method.  The  nitrous  acid 
in  the  gases  may  then  be  determined  by  rinsing  out  the  contents 
of  the  absorption  bottle  A  into  a  flask,  adding  a  drop  of  phenol- 
phthalein,  and  titrating  the  free  acetic  acid  with  a  decinormal 
solution  of  sodium  hydroxide.  From  the  volume  of  the  sodium 
hydroxide  solution  used,  there  is  to  be  subtracted  10  cc.  for  the 
hydriodic  acid  resulting  from  the  reduction  of  the  10  cc.  of  deci- 
normal iodine  solution,  and  also  10  cc.  more  for  the  sulphuric 
acid  formed  in  the  reaction  (see  page  274).  The  balance  of  the 
sodium  hydroxide  that  is  used  indicates  free  nitric  acid  or  nitrous 
acid.  Raschig  states  that  while  the  method  gives  satisfactory 
results  for  sulphur  dioxide,  it  is  not  very  exact  for  the  determina- 
tion of  the  oxides  of  nitrogen  if  the  gas  sample  is  taken  from  the 
beginning  of  the  lead  chambers,  because  here  the  sulphur  dioxide 
is  present  in  preponderating  amount.  If,  however,  the  gas 
sample  is  taken  from  the  end  of  the  chamber  system  where  the 
oxides  of  nitrogen  are  present  in  much  larger  proportion,  a  pro- 
portionately larger  sample  of  the  gases  will  be  needed  to  de- 
colorize the  iodine  solution  and  a  determination  of  the  oxides 
of  nitrogen  will  be  correspondingly  more  exact. 

CARBON  OXYSULPHIDE    (COS) 

Properties    of    Carbon   Oxysulphide.  —  Specific  gravity, 
2.0749;  weight  of  one  liter,  2.6825  grams. 
Pure  carbon  oxysulphide  has  no  odor,  and  its  freshly  prepared 


278 


GAS  ANALYSIS 


solution  in  water  has  no  taste.  Its  action  upon  the  nervous 
system  is  somewhat  similar  to  that  of  nitrous  oxide.1  When 
inhaled  for  a  few  seconds  it  causes  dizziness  and  buzzing  in  the 
ears,  but  if  the  inhalation  is  not  continued,  the  symptoms  quickly 
disappear. 

Water  absorbs  about  one-third  2  of  its  own  volume  of  the  gas. 

A  solution  of  potassium  hydroxide  absorbs  carbon  oxysulphide 
very  slowly,  but  the  gas  is  rapidly  taken  up  by  a  solution  pre- 
pared by  dissolving  one  part  of  potassium  hydroxide  in  two  parts 
of  water  and  adding  an  equal  volume  of  alcohol.  The  analyt- 
ical absorbing  power  of  this  solution  is  18;  that  is,  a  cubic 
centimeter  of  this  reagent  is  able  to  absorb  72  cc.  of  carbon 
oxysulphide.  The  gas  is  but  slightly  soluble  in  a  hydrochloric 
acid  solution  of  cuprous  chloride,  i  cc.  of  this  solution  absorbs 
about  0.2  cc.  of  the  gas. 

Experiments  made  by  Hempel 3  upon  the  analytical  absorb- 
ing power  of  various  reagents  for  carbon  oxysulphide,  hydrogen 
sulphide,  and  carbon  bisulphide  gave  the  following  results: 


ANALVTI 

CAL  ABSORBINC 

;  POWER 

REAGENT  EMPLOYED 

Carbon 
Oxysulphide 

Hydrogen 
bulpnide 

Carbon 
Bisulphide 

Chloroform      
A/r,Vt,     >    )  T  Part  triethylphosphine     . 

I 

2   3 
-ff. 

Ml*ture    i  9  parts  chloroform    .      .      . 
Pyridinc 

I    ' 
I  .  I 

4-5 

(  i  part  triethylphosphine     . 
Mixture    <  9  parts  pyridine        .     .      . 
(  10  parts  nitrobenzene 
Nitrobenzene  
i  part  potassium  hydroxide  in  2  parts 
water.    One-half  saturated  with  H2S, 

(          3 
3 

26 

2 

26 
46 

and  the  2  portions  then  mixed 
Saturated  solution  of  copper  sulphate  in 
a  mixture  of  200  grams  water  and  200 

1  Klason,  J.  prakt.  Chem.  36  (1887),  64. 

2  Witzeck,  /.  Gasbeleuchtung,  46  (1903),  145. 

3  Z.f.  angewandte  Chem.  1901,  865. 


PROPERTIES  OF  THE  VARIOUS   GASES  279 

Carbon  oxysulphide  may  be  separated  from  hydrogen  sul- 
phide by  absorbing  the  latter  in  an  acidulated  solution  of  copper 
sulphate  (see  table  above).  Separation  from  vapor  of  carbon 
bisulphide  may  be  effected  by  passing  the  gases  through  a  mix- 
ture of  one  part  of  triethylphosphine  and  nine  parts  of  chloro- 
form, which  absorbs  the  carbon  bisulphide.  The  most  delicate 
reagent  for  its  detection  is  iodide  of  starch.  If  the  gas  is  passed 
through  a  starch  solution  that  is  colored  a  clear  blue  by  a  trace 
of  iodine,  the  color  of  the  solution  is  very  slowly  discharged. 
The  blue  tint  changes  first  to  violet,  then  to  red,  and  finally  the 
color  disappears  completely.  Other  gases  that  would  act  upon 
the  iodide  of  starch  must  of  course  be  absent. 

One  volume  of  carbon  oxysulphide  needs  ij  volumes  of 
oxygen  for  its  combustion  and  yields  one  volume  of  COz  and 
one  volume  of  SO2. 

Determination  of  Carbon  Oxysulphide.  —  Hempel  deter- 
mines 1  carbon  oxsulphide  in  the  presence  of  hydrogen  sulphide 
and  carbon  dioxide  by  first  absorbing  the  hydrogen  sulphide 
with  an  acid  solution  of  copper  sulphate,  then  decomposing 
the  carbon  oxysulphide  into  carbon  monoxide  and  sulphur  by 
passing  the  residual  gas  mixture  through  a  hot  capillary  tube 
of  platinum,  determining  the  carbon  monoxide  that  is  here  set 
free  by  absorption  in  a  hydrochloric  acid  solution  of  cuprous 
chloride,  and  finally  determining  the  carbon  dioxide  by  means  of 
potassium  hydroxide. 

Witzeck  2  raises  objections  to  this  method  and  gives  prefer- 
ence to  the  procedure  proposed  by  Lunge,  which  consists  in 
passing  the  gas  mixture  through  an  iodine  solution  for  the  re- 
moval and  the  determination  of  hydrogen  sulphide,  and  then 
shaking  the  residual  gas  with  a  solution  of  potassium  hydroxide 
which  will  decompose  the  carbon  oxysulphide  with  the  forma- 
tion of  potassium  sulphide  and  potassium  carbonate.  To  this 
solution  hydrochloric  acid  is  then  added  to  set  free  hydrogen 

1  Z.  /.  angewandte  Chem.  1901,  865. 

2  Loc.  cit. 


2 So  GAS  ANALYSIS 

sulphide  and  carbon  dioxide.  The  hydrogen  sulphide  is  deter- 
mined by  means  of  an  iodine  solution  and  the  carbon  dioxide  is 
determined  by  absorption  with  potassium  hydroxide.  Since  one 
volume  of  carbon  oxysulphide  yields  upon  decomposition  one 
volume  of  hydrogen  sulphide  and  one  volume  of  carbon  dioxide, 
the  amount  of  carbon  dioxide  present  in  the  original  mixture 
is  ascertained  by  subtracting  from  the  volume  of  carbon  dioxide 
formed,  a  volume  equal  to  that  of  the  hydrogen  sulphide  found 
to  be  present. 

Carbon  oxysulphide  cannot  be  present  in  washed  illuminating 
gas  because  as  Witzeck  points  out  it  will  be  completely  decom- 
posed by  the  water  vapor  with  which  it  comes  in  contact.  Even 
if  it  should  partially  escape  decomposition  by  water  it  would 
react  very  rapidly  with  ammonia  or  with  ammonium  hydroxide 
to  form  ammonium  thiocarbamate, 

~    /ONH4 


S=C  =0  +  3  , 

Vlv 


FLUORINE     Ft) 

Determination  of  Fluorine.  —  O.  W.  F.  Oettel  devised  a 
method  for  the  determination  of  fluorine  in  a  substance,  the 
fluorine  being  evolved  as  silicon  tetrafluoride,  and  the  volume 
of  this  gas  then  being  directly  measured.  Since  a  large  number 
of  substances  contain  both  fluorine  and  carbon  dioxide,  Hempel 
and  W.  Scheffler  1  have  modified  the  method  to  permit  of  the 
simultaneous  determination  of  fluorine  and  carbon  dioxide  in  a 
single  sample. 

The  fluorine  is  set  free  as  silicon  tetrafluoride  together  with 
carbon  dioxide  in  a  suitable  apparatus,  is  collected  in  a  burette, 
and  the  silicon  tetrafluoride  is  then  decomposed  and  absorbed 
by  means  of  water  (a  small  volume  of  carbon  dioxide  is  here 
taken  up  by  the  water).  The  carbon  dioxide  still  present  in  the 
gas  is  then  completely  removed  by  passing  the  gas  into  a  pipette 
containing  caustic  potash.  The  gas  residue  is  again  brought 

1Z.f.  anorg.  Chem.,  20  (1899),  i. 


PROPERTIES   OF  THE  VARIOUS   GASES  281 

over  the  water  which  was  first  used  and  by  which  the  silicon 
tetrafluoride  was  absorbed;  the  absorbed  carbon  dioxide  here- 
upon escapes  from  the  water  and  passes  into  the  gas  residue. 
Upon  transferring  the  gas  once  more  to  the  caustic  potash  pi- 
pette, the  remainder  of  the  carbon  dioxide  is  removed,  and  this 
volume  is  subtracted  from  the  diminution  first  obtained  by  the 
absorption  with  water.  The  difference  gives  the  amount  of  sili- 
con tetrafluoride.  In  this  manner  it  is  possible  to  make  very 
sharp  determinations  of  fluorine  in  the  presence  of  carbon 
dioxide. 

For  setting  free  the  silicon  tetrafluoride  there  is  used  the  ap- 
paratus shown  in  Fig.  87,  II.  The  evolution  flask  is  connected 
with  a  simple  gas  burette  filled  with  mercury  and  containing  on 
top  of  the  mercury  some  concentrated  sulphuric  acid.  It  is  well 
to  join  to  the  burette  a  level-bulb  instead  of  a  level-tube,  and  to 
attach  a  glass  stopcock  to  the  lower  end  of  the  burette  tube 
(see  Fig.  87). 

The  substance  under  examination  is  mixed  with  finely  pow- 
dered quartz,  the  weight  of  the  quartz  being  fifteen  times  that 
of  the  fluorine  which  is  probably  present  in  the  material.  The 
quartz  is  first  heated  for  a  long  time  in  a  muffle  furnace  with 
free  access  of  air  to  remove  every  trace  of  organic  matter. 

The  sulphuric  acid  to  be  employed  must  be  freed  from  or- 
ganic substances  and  from  oxides  of  nitrogen.  This  is  ac- 
complished by  adding  to  concentrated  sulphuric  acid  about 
5  grams  of  powdered  sulphur  and  then  fuming  down  the  acid  to 
two-thirds  of  its  original  volume. 

In  carrying  out  a  determination  the  evolution  flask  II  is  first 
carefully  dried  and  the  substance,  together  with  the  proper 
amount  of  quartz  powder,  is  then  introduced  into  the  flask  by 
means  of  a  long  weighing  tube,  and  the  two  powders  are  mixed 
as  intimately  as  possible  by  shaking  the  flask.  The  flask  is  then 
joined  by  means  of  the  capillary  d  and  a  piece  of  dry  rubber 
tubing  to  the  gas  burette  I  which  contains  mercury  and  some 
sulphuric  acid,  as  above  described.  The  rubber  tube  is  held 


282 


GAS  ANALYSIS 


firmly  in  place  by  means  of  ligatures  of  light  wire.  The  vol- 
ume of  concentrated  sulphuric  acid  which  is  placed  in  the  bu- 
rette amounts  to  only  about  0.25  cc.  Its  presence  is  necessary 
to  avoid  the  possibility  of  decomposition  of  the  silicon  tetra- 
fluoride  by  any  moisture  that  might  be  in  the  burette. 

ST 


FIG.  87 

In  the  bells  I  and  m  is  placed  some  of  the  highly  concentrated 
sulphuric  acid.  A  water  suction  pump  is  now  connected  to  k, 
and  the  flask  II  is  partially  exhausted.  The  stopcock  n  is  then 
closed,  and  upon  lifting  the  tube  o  sulphuric  acid  flows  down 
from  m  into  the  flask.  The  flask  is  shaken  so  as  to  bring  the 
acid  into  intimate  contact  with  the  mixture  of  quartz  and  the 


PROPERTIES  OF  THE  VARIOUS  GASES 


283 


substance,  and  the  contents  of  the  flask  is  then  heated  fully  up 
to  the  boiling-point  of  sulphuric  acid,  the  heating  being  con- 
tinued for  about  fifteen  minutes. 

If  the  apparatus  should  break,  the  operator  might  be  seriously 
injured  by  the  hot  concentrated  sulphuric  acid.  It  is  well, 
therefore,  to  protect  the  eyes  with  goggles,  and  to  place  a  glass 
screen  between  the  flask  and  the  operator. 

The  heating  is  now  stopped, 
and  the  gas  in  the  flask  is  com- 
pletely driven  over  into  the 
burette  by  filling  m  with  con- 
centrated sulphuric  acid  and 
carefully  lifting  the  tube  o. 
The  flask  is  then  disconnected 
from  the  burette  and  the  total 
volume  of  the  gas  is  measured. 

The  burette  is  now  con- 
nected in  the  ordinary  man- 
ner, by  means  of  a  capillary 
tube,  with  a  simple  mercury 
absorption  pipette  of  the  form 
shown  in  Fig.  88,  the  pipette 
containing  5  cc.  of  water  above 
the  mercury.  The  gas  is  trans- 
ferred to  the  pipette  and 
shaken  for  five  minutes  with  FIG.  gg 

the  water.    It  is  then  brought 
back  into  the  burette  and  the  diminution  in  volume  is  read  off. 

The  remaining  gas  is  passed  into  a  pipette  filled  with  a  solu- 
tion of  potassium  hydroxide  to  absorb  carbon  dioxide,  and  is 
then  drawn  back  into  the  gas  burette.  The  volume  is  observed, 
and  the  gas  is  now  passed  into  the  first  pipette,  Fig.  88,  and 
shaken  again  for  three  minutes.  It  is  then  passed  back  into 
the  burette,  and  the  residual  volume  of  gas  is  measured.  This 
gas  is  then  passed  once  more  into  the  potassium  hydroxide 


284 


GAS  ANALYSIS 


pipette  to  determine  the  small  amount  of  carbon  dioxide  which 
was  taken  up  by  the  water  used  in  the  first  absorption  of  the 
silicon  tetrafluoride. 

All  of  these  operations  can  be  carried  out  with  considerable 
speed,  and  it  is  therefore  easily  possible  to  make  a  determination 
of  fluorine  in  two  hours. 

As  an  example  of  the  accuracy  of  the  method,  the  following 
result  may  be  cited:  2.156  grams  of  the  substance  gave  3.56  cc. 
of  silicon  tetrafluoride,  while  theory  called  for  3.45  cc. 

To  illustrate  the  application  of  the  method  to  the  analysis 
of  teeth,  a  few  results  of  determinations  of  fluorine  in  teeth  ash 
are  tabulated  below. 

The  incineration  of  teeth  is  easily  effected  in  a  hard  glass  tube 
in  a  current  of  oxygen  if  the  powder  is  very  fine  and  is  placed 
in  the  tube  in  a  very  thin  layer. 

In  determining  fluorine  in  material  that  contains  organic 
matter,  it  is  very  important  that  the  substance  should  be  com- 
pletely incinerated,  since  the  slightest  trace  of  residual  carbon 
would  act  upon  the  boiling  sulphuric  acid  and  cause  the  forma- 
tion of  sulphur  dioxide,  a  gas  which  would  then  be  absorbed  by 
water  when  the  silicon  tetrafluoride  is  determined. 


CO2 

SiF4 

Per  cent 

HUMAN 
TEETH 

Grams 
of 
Teeth 
Ash 
taken 

SiF4 
+ 
C02 
found 

CO2 

which 
was 
taken  up 
by  the 
water 

in 
cubic 
centi- 
meters 

Fluorine 
in 
Grams 

of 
Fluorine 
in   the 
Teeth 
Ash 

Unsound 

1-793 

I  .O 

4-65 

1.0 

0.0034 

O.IQ 

Sound 

1-434 

i-5 

5-8o 

O.I 

1.4 

0.0047 

0-33 

Sound 

0.831 

1.6 

3-50 

1.6 

0.0054 

0.52 

CHLORINE   (C12) 

Properties  of  Chlorine.  —  Specific  gravity,  2.4494;  weight  of 
one  liter,  3.166  grams. 

Chlorine  is  quite  soluble  in  water.    One  part  of  cold  water 


PROPERTIES  OF  THE   VARIOUS   GASES  285 

dissolves  approximately  two  volumes  of  chlorine;  hot  water 
dissolves  less.  According  to  Schonfeld,  one  volume  of  water 
absorbs  the  following  volumes  of  chlorine:  — 

10°,  2.5852 
15°,  2.3681 

20°,  2.1565 
25°,  1.9504 
30°,  1.7499 

35°,  1-5550 
40°,  1.3656. 

Determination  of  Chlorine.  —  Chlorine  may  be  determined 
by  the  Bunsen  procedure,  in  which  the  gas  is  led  through  a  solu- 
tion of  potassium  iodide,  and  the  iodine  set  free  is  titrated  with 
sodium  thiosulphate :  — 

C12    +   2  KI    =    2  KC1    +   2  I 

2  Na2S2O3  +  2  I  =  Na2S4O6  +  2  Nal. 

Chlorine  is  absorbed  by  potassium  hydroxide  or  sodium 
hydroxide.  In  cold  dilute  solutions  the  hypochlorite  and 
chloride  of  the  alkali  are  formed :  — 

2  KOH  +  C12  =  KC1O  +  KC1  +  H2O. 
In  hot  concentrated  solutions,  the  reaction  is:  — 

6  KOH  +  3  C12  =5  KC1  +  KC1O3  +  3  H2O. 

The  first  of  these  two  reactions  was  used  by  Treadwell  in  the 
determination  of  chlorine  in  the  presence  of  carbon  dioxide,  but 
Offerhaus  1  found  that  even  with  a  very  dilute  solution  of  sodium 
hydroxide  an  appreciable  amount  of  sodium  chlorate  is  formed, 
and  that  for  this  reason  the  titration  of  the  hypochlorite  with 

—  arsenious  acid  gives  results  about  0.7  per  cent  too  low. 

1  Z.f.  angewandte  Chem.,  16  (1903),  1033. 


286  GAS  ANALYSIS 

Offerhaus  obtained  very  satisfactory  results  by  passing  the 
mixture  of  chlorine  and  carbon  dioxide  through  two  dry  Bunte 
burettes  connected  in  series,  determining  chlorine  in  the  first 
burette  by  absorbing  the  gas  with  a  solution  of  potassium  iodide 
and  titrating  the  liberated  iodine,  and  in  the  second  burette 
determining  the  total  amount  of  chlorine  and  carbon  dioxide  by 

absorption  of  the  two  gases  with  — •  sodium  hydroxide.     The 

difference  between  the  two  results  gives  the  amount  of  carbon 
dioxide. 

To  avoid  the  use  of  two  gas  burettes,  Treadwell  and  Christie  l 
absorb  the  chlorine  in  a  decinormal  solution  of  primary  potas- 
sium arsenite,  KH^AsOs,  and  directly  afterward  determine  the 
carbon  dioxide  in  the  gas  mixture  by  absorption  with  a  solution 
of  potassium  hydroxide. 

They  used  a  water- jacketed  Bunte  burette  with  a  tail-stopcock 
at  G  (see  Fig.  43)  as  well  as  at  C,  and  with  the  upper  part  of 
the  burette  narrow  to  render  more  accurate  the  reading  of  small 
residual  gas  volumes.  The  burette  is  cleaned  and  thoroughly 
dried,  and  the  gas  mixture  is  then  passed  into  the  burette 
through  the  end  of  the  lower  stopcock  and  out  through  the  upper 
stopcock,  the  passage  of  the  gas  being  continued  until  all  of  the 
air  that  was  originally  in  the  burette  has  been  displaced.  The 
lower  stopcock  is  then  closed  and  after  ten  seconds  the  upper 
stopcock  is  closed  and  the  barometric  pressure  and  temperature 
of  the  water  surrounding  the  burette  are  noted.  The  lower 
stopcock  is  then  turned  so  that  the  upper  end  of  the  stopcock 
communicates  with  the  tube  H  from  the  level-bottle  B.  Tread- 
well  and  Christie  use  a  level-tube  in  place  of  the  level-bottle. 
The  level-tube  is  filled  with  distilled  water  and  this  is  allowed  to 
flow  through  the  rubber  tube  H  and  out  through  the  end  of  the 
lower  stopcock  G  to  expel  air  from  the  tube  and  chlorine  from 
the  end  tube  and  lower  stopcock.  When  the  water  has  flowed 
out  of  the  level-tube  and  only  the  connecting  rubber  tube  H  is 

1  Z.  /..  angewandte  Chem.,  18  (1905),  1930. 


PROPERTIES  OF  THE  VARIOUS   GASES  287 

filled  with  water,  the  stopcock  G  is  closed  and  there  is  poured 
into  the  level-tube  exactly  100  cc.  of  a  decinormal  solution  of 
primary  potassium  arsenite.  This  solution  is  prepared  by  dis- 
solving 4.95  grams  of  arsenic  trioxide  in  a  dilute  solution  of 
potassium  hydroxide,  adding  phenolphthalein  and  then  sul- 
phuric acid  until  the  color  of  the  solution  disappears,  and  finally 
diluting  to  one  liter.  The  lower  stopcock  is  then  turned  so  that 
the  level-tube  communicates  with  the  burette.  The  arsenite 
solution  at  first  rises  rather  slowly  in  the  burette,  but  later  its 
passage  is  more  rapid.  Toward  the  close  of  the  absorption  of 
the  chlorine,  the  burette  is  shaken  to  hasten  the  completion  of 
the  reaction. 

After  the  absorption  of  the  chlorine  has  been  effected,  which 
takes  about  5  minutes,  the  liquid  in  the  two  tubes  is  brought  to 
the  same  height  and  the  volume  of  gas  remaining  in  the  burette 
is  read  off.  The  level-tube  is  now  lowered,  10  cc.  of  a  solution  of 
potassium  hydroxide  (i  12)  is  poured  into  the  funnel  D,  the  upper 
stopcock  C  is  carefully  opened  and  the  solution  drawn  down  into 
the  burette.  The  stopcock  is  then  closed,  the  burette  is  shaken 
to  hasten  the  absorption  of  the  carbon  dioxide,  the  liquid  in  the 
burette  and  level-tube  is  brought  to  the  same  height  and  the 
residual  gas  volume  is  read  off  the  temperature  and  barometric 
pressure  being  again  noted. 

All  of  the  liquid  in  the  level-tube  and  in  the  burette  is  then 
transferred  to  an  Erlenmeyer  flask  and  the  apparatus  thoroughly 
rinsed  with  water  which  is  also  added  to  the  contents  of  the  flask. 
Some  phenolphthalein  is  then  added  to  the  solution  and  dilute 
hydrochloric  acid  (1:4)  is  run  in  until  the  red  color  of  the  liquid 
just  disappears.  60  cc.  of  a  solution  of  sodium  bicarbonate 
containing  40  grams  of  the  salt  to  the  liter  is  then  added  to- 
gether with  a  little  starch  solution,  and  the  excess  of  arsenious 

acid  is  determined  by  titration  with  ^  solution  of  iodine. 

In  calculating  the  results,  allowance  must  be  made  for  the  fact 
that  the  original  mixture  of  chlorine  and  carbon  dioxide  is 


288  GAS  ANALYSIS 

usually  practically  free  from  moisture,  while  the  gas  residue  in 
the  burette  is  measured  in  the  moist  condition.  The  volume 
which  the  residual  gas  would  occupy  if  dry  and  at  the  pressure 
and  temperature  under  which  the  gas  sample  was  measured 
must  consequently  first  be  calculated.  The  difference  between 
this  volume  and  the  original  volume  of  the  sample  in  the  burette 
will  give  the  total  amount  of  chlorine  and  carbon  dioxide.  The 
amount  of  chlorine  may  be  read  off  after  the  absorption  of  that 
gas  by  the  arsenite  solution  and  the  correction  of  the  residual 
volume,  or  it  may  be  determined  by  titration  with  an  iodine 

solution  as  above  mentioned.     One  cc  of  an  --  solution  of 

10 

iodine  corresponds  to  0.003546  gram  chlorine,  and  this  weight 
of  chlorine  under  standard  conditions  will  occupy  a  volume  of 
1.1015  cc< 

Treadwell  and  Christie  state  that  the  determination  of  chlorine 
by  absorption  with  the  arsenite  solution  agrees  quite  closely 
with  the  results  obtained  by  titration,  the  average  difference 
amounting  to  0.13  per  cent. 

If  a  solution  contains  free  chlorine  together  with  hydro- 
chloric acid,  they  may  both  be  determined  in  the  following 
manner  (Fresenius) :  — 

To  a  weighed  portion  of  the  liquid  add  an  aqueous  solution  of 
sulphurous  acid  until  the  latter  is  in  excess ;  after  some  time  add 
nitric  acid  and  then  some  potassium  chromate  to  destroy  the 
excess  of  sulphur  dioxide,  and  precipitate  the  total  chlorine  as 
silver  chloride. 

If  now  the  amount  of  free  chlorine  is  determined  in  a  second 
portion  by  potassium  iodide,  the  difference  gives  the  quantity 
of  chlorine  present  in  the  form  of  chloride. 

The  total  chlorine  may  be  volumetrically  determined  by  ab- 
sorbing the  gases  with  a  solution  of  sodium  hydroxide,  adding 
sulphur  dioxide,  then,  after  a  while,  nitric  acid  and  some  potas- 
sium chromate,  and  finally  neutralizing  the  solution  by  adding 
calcium  carbonate.  All  chlorine  is  now  present  as  chloride,  and 


PROPERTIES   OF  THE   VARIOUS   GASES 


289 


the  solution  is  neutral,  so  that  the  chlorine  may  be  titrated  with  a 
neutral  silver  solution,  potassium  chromate  being  used  as  in- 
dicator. 

HYDROGEN   CHLORIDE    (HC1) 

Properties  of  Hydrogen  Chloride. —  Specific  gravity,  1.2595; 
weight  of  one  liter,  1.6283  grams. 

According  to  Roscoe  and  Dittmar,  one  volume  of  water  dis- 
solves at  o°,  503  volumes  of  hydrogen  chloride.  The  parts  by 
weight  of  the  gas  which  dissolve  in  one  gram  of  water  at  a 
pressure  of  760  mm.  and  at  different  temperatures,  are  given  in 
the  following  table:  — 


TEMPERATURE 

HC1 

TEMPERATURE 

HC1 

O 

0.825 

32 

0.665 

4 

0.804 

36 

0.649 

8 

0.783 

40 

0.633 

12 

0.762 

44 

0.618 

16 

0.742 

48 

0.603 

20 

0.721 

52 

0.589 

24 

0.700 

56 

0-575 

28 

0.682 

60 

0.561 

At  ordinary  temperatures,  one  volume  of  alcohol  dissolves  327 
volumes  of  hydrogen  chloride. 

Determination  of  Hydrogen  Chloride. —  If  no  other  acid  gas 
is  present  with  the  hydrogen  chloride,  it  may  be  determined  by 
drawing  a  measured  quantity  of  the  gas  through  a  standardized 
solution  of  an  alkali  and  titrating  back  with  an  acid. 

Hydrogen  chloride  may  also  be  determined  by  absorbing  it 
with  an  alkaline  solution  free  from  chlorine,  and,  after  acidifying, 
precipitating  it  with  silver  nitrate,  and  weighing  as  silver  chlo- 
ride. 

A  method  proposed  by  Cl.  Winkler,1  and  based  upon  J.  Vol- 
hard's  volumetric  method  for  the  determination  of  silver,2  con- 

1  Cl.  Winkler,  Anleitung  zur  Untersuchung  der  Industrie-Case,  Part  II,  p.  322. 

2  J.  Volhard,  Zeitschrijt  fur  andyt.  Chemie,  13  (1874),  171,  and  17  (1878),  482. 


29o  GAS   ANALYSIS 

sists  in  placing  in  a  suitable  absorption  apparatus  a  few  drops 
of  ammonium  sulphocyanate  or  potassium  sulphocyanate,  some 

iron  alum  solution,  and  a  measured  amount  of  —  silver  nitrate 

10 

solution.  Upon  leading  the  gas  through  this  solution  the  hydro- 
chloric acid  reacts  with  the  silver,  forming  silver  chloride.  The 
end  of  the  reaction  is  shown  by  the  blood-red  color.  The  ap- 
pearance of  this  color  is  due  to  the  fact  that  after  all  of  the  sil- 
ver nitrate  has  been  changed  to  silver  chloride,  the  silver  sul- 
phocyanate present  is  also  decomposed  and  ferric  sulphocyanate 
is  formed.  The  volume  of  the  gas  is  measured  and  the  amount 
of  hydrogen  chloride  that  it  contains  is  calculated. 

SILICON  TETRAFLUORIDE    (SiF4) 

Specific  gravity,  3.60;  weight  of  one  liter,  4.663  grams. 

The  gas  is  completely  absorbed  by  water,  and  is  at  the  same 
time  decomposed  — 

3  SiF4  +  4  H2O  =  Si  (OH)4  +  2  H2SiF6. 

This  reaction,  which  has  been  employed  by  R.  Fresenius  1 
for  the  quantitative  determination  of  fluorine,  might  possibly 
be  made  use  of  for  the  determination  of  silicon  tetrafluoride  in 
gases. 

PHOSPHINE    (PH3) 

Properties  of  Phosphine.  —  Specific  gravity,  1.175;  weight  of 
one  liter,  1.52  grams. 

Phosphine  is  a  colorless  gas  with  a  very  unpleasant  odor  re- 
sembling that  of  decayed  fish.  It  is  very  poisonous.  The  pure 
gas  takes  fire  only  at  a  temperature  above  100  .  It  can  be  mixed 
with  pure  oxygen  without  change,  but  if  the  mixture  be  sud- 
denly brought  under  diminished  pressure,  it  explodes.  Phosphine 
takes  fire  when  brought  in  contact  with  a  drop  of  fuming  ni- 
tric acid,  or  writh  chlorine  or  bromine. 

1  Fresenius,  Quant,  chemische  Analyse,  6th  ed.,  Part  I,  p.  431. 


PROPERTIES  OF  THE  VARIOUS   GASES  291 

Phosphine  is  somewhat  soluble  in  water.  One  volume  of  water 
absorbs  about  0.02  volume  of  the  gas,  and  takes  on  its  odor  and 
a  disgusting  taste.  Exposed  to  the  light,  the  solution  decom- 
poses with  evolution  of  hydrogen  and  separation  of  amorphous 
phosphorus.  The  gas  is  decomposed  by  the  electric  spark  into 
phosphorus  and  hydrogen. 

When  a  strip  of  silver  nitrate  test  paper  is  brought  into  con- 
tact with  the  gas,  the  paper  is  at  once  blackened,  metallic  silver 
and  phosphoric  acid  being  formed. 

If  phosphine  is  passed  through  a  neutral  aqueous  solution 
of  potassium  mercuric  iodide,  a  crystalline,  orange-yellow  pre- 
cipitate, PHg3I3,  is  produced.1 

Determination  of  Phosphine.  —  Phosphine  may  be  deter- 
mined by  converting  it  into  phosphoric  acid  either  by  burning 
it  or  by  passing  it  through  bromine  water  or  a  solution  of  sodium 
hypochlorite  and  precipitating  the  resulting  phosphoric  acid 
with  magnesia  mixture.  These  reactions  may  also  be  utilized 
for  the  detection  of  phosphine  in  a  gas  mixture,  the  phosphoric 
acid  being  identified  by  precipitation  with  ammonium  mo- 
lybdate. 

Further  details  concerning  the  determination  of  phosphine, 
particularly  in  the  presence  of  acetylene,  are  given  on  p.  360. 

ARSINE  (AsH3) 

Properties  of  Arsine.  —  Specific  gravity,  2.696;  weight  of  one 
liter,  3.485  grams. 

Arsine  is  a  colorless  gas  of  very  unpleasant  odor.  It  is  ex- 
tremely poisonous.  When  passed  through  a  highly  heated 
tube,  the  gas  is  decomposed  and  a  glistening  mirror  of  metallic 
arsenic  is  deposited.  The  gas  is  slightly  soluble  in  water. 

The  best  confining  liquid  for  gas  mixtures  that  may  contain 
arsine  is  a  freshly  boiled  concentrated  solution  of  sodium  chlo- 
ride. Arsine  is  completely  and  rapidly  absorbed  by  solutions  of 

1  Lemoult,  Compt.  rend.,  139  (1904),  478. 


292  GAS  ANALYSIS 

silver  nitrate.  The* reaction  with  dilute  neutral  silver  nitrate  or 
with  a  slightly  acid  solution  of  this  salt  does  not  quantitatively 
proceed  according  to  the  Lassaigne  1  reaction 

AsH3  +  6  AgNO3  +  3  H2O  =  H3AsO3  +  6  Ag  +  6  HNO3 
but  in  part  follows  the  equation:  — 

AsH3  +  3  AgNO3  =  AsAg3  +  3  HN03. 

In  the  presence  of  an  excess  of  silver  nitrate  the  silver  ar- 
senide formed  in  the  preceding  reaction  gradually  undergoes 
change  as  follows: 

AsAg3  +  3  AgNO3  +  3  H20  =  H3AsO3  +  6  Ag  +  3  HNO3. 

In  dilute  ammoniacal  silver  solution  three  reactions  appear  to 
occur: 

(a)  AsH3  +  3  (AgNH3)  N03  =  AsAg3  +  3  NH4N03, 

(b)  AsAg3  +  3  (AgNH3)  NO3  +  NH4OH  +  H2O  - 

NH4AsO2  +  6  Ag  -f  3  NH4NO3, 

(c)  NH4As02  +  2  (AgNH3)  NO3  +  2  NH4OH  = 

(NH4)3  As04  +  2  Ag  +  2  NH4N03. 

If,  however,  the  solution  is  heated  for  some  time  after  absorp- 
tion, the  end  reaction  may  be  expressed  by  the  equation: 

AsH3  +  8  (AgNH3)  NO3  +  3  NH4OH  +  H2O  = 
(NH4)3  AsO4  +  8  Ag  +  8  NH4NO3. 

When  metallic  arsenic  stands  in  contact  with  an  ammoniacal 
silver  solution  and  the  solution  is  warmed,  the  arsenic  is  oxidized 
to  arsenic  acid.2 

As  +  5  (AgNH3)  N03  +  3  NH4OH  +  H2O  = 
(NH4)3  As04  +  5  Ag  +  5  NH4NO3. 

1  J.  chim.  medic.,  16  (1840),  685. 

2  Most  of  the  above  details  are  from  the  article  by  Reckleben,  Lockemann  and 
Eckardt,  Z.f.  analyt.  Chetn.,  46  (1907),  671. 


PROPERTIES  OF  THE  VARIOUS   GASES  293 

Detection  of  Arsine.  —  Arsine  may  be  detected  by  allowing 
the  gas  to  act  upon  a  crystal  of  silver  nitrate.  If  the  amount 
of  arsine  in  the  gas  mixture  under  examination  is  not  too 
great,  there  is  formed  a  yellow  compound  which  is  said  to  be 
AsAg3-  3  AgNO3.  If  the  gas  contains  considerable  arsine,  the 
yellow  color  appears  only  for  an  instant  and  changes  to  black 
almost  immediately.  If  the  gas  mixture  contains  hydrogen 
sulphide,  this  is  removed  by  passing  the  gases  through  a  glass 
tube  that  contains  first  a  plug  of  cotton,  then  a  second  plug  of 
cotton  that  has  been  moistened  with  a  solution  of  ammonium 
lead  acetate,  and  beyond  this  a  crystal  of  silver  nitrate  and  one 
of  lead  acetate.  The  latter  serves  to  show  whether  any  hydro- 
gen sulphide  has  passed  the  second  cotton  plug. 

Arsine  may  also  be  detected  1  by  passing  the  gas  into  a  rather 
concentrated  ammoniacal  silver  solution  which  is  at  once 
darkened  by  the  slightest  traces  of  the  gas.  The  test  does  not 
serve  to  detect  arsine  in  the  presence  of  stibine,  phosphine,  or 
hydrogen  sulphide,  because  those  gases  also  cause  a  darkening 
of  the  silver  solution. 

Determination  of  Arsine.  —  Arsine  cannot  accurately  be  de- 
termined by  passing  the  gas  into  a  solution  of  silver  nitrate  and 
ascertaining  either  the  amount  of  silver  precipitated  or  of  ar- 
senious  acid  formed.2  It  may,  however,  be  volumetrically  de- 
termined by  absorbing  the  gas  with  a  neutral  solution  of  silver 
nitrate  or  with  a  solution  of  sodium  hypochlorite  containing 
three  per  cent  of  active  chlorine. 

STIBINE  (SbH3) 

Specific  gravity,  4.33;  weight  of  one  liter,  5.6  grams. 

Stibine  is  a  colorless  gas  of  less  pronounced  odor  than  arsine. 
It  is  but  slightly  soluble  in  water. 

When  stibine  is  passed  into  a  solution  of  silver  nitrate  a  black 
precipitate,  SbAg3,  is  formed.  If  this  substance  is  washed  with 

1  Reckleben  and  Lockemann,  Z.f.  angew.  Chcm.,  19  (1906),  275. 

2  Reckleben  and  Lockemann,  loc.  cit. 


294  GAS  ANALYSIS 

water  and  boiled  with  tartaric  acid,  it  is  decomposed  with  the 
formation  of  silver  and  a  soluble  compound  of  antimony. 

When  stibine  acts  upon  a  crystal  of  silver  nitrate,  the  black 
compound,  SbAg3,  is  formed. 

Stibine  may  be  determined  by  passing  the  gas  into  a  solution 
of  silver  nitrate,  collecting  the  silver  antimonide  on  a  filter, 
washing  it,  decomposing  it  with  tartaric  acid  and  determining 
the  antimony  in  solution. 


CHAPTER  XIV 
FLUE  GAS  ANALYSIS 

In  the  examination  of  the  efficiency  of  the  various  devices  in 
which  the  chemical  energy  of  the  fuel  is  transformed  into  heat 
energy,  it  is  usually  necessary  to  determine  the  composition  and 
the  heating  value  of  the  fuel,  and  to  make  an  analysis  of  the  gas 
mixture  that  passes  from  the  zone  of  combustion  into  the  flue. 
The  analysis  of  solid  and  liquid  fuels  does  not  fall  within  the 
scope  of  the  present  work,  but  the  analysis  of  flue  gas  will  here 
be  considered,  and  the  determination  of  the  heating  value  of 
solid,  liquid  and  gaseous  fuel  and  the  analysis  of  combustible 
gas  mixtures  will  be  discussed  in  later  chapters. 

When  carbon  is  burned  in  air,  one  volume  of  oxygen  unites 
with  solid  carbon  to  form  one  volume  of  carbon  dioxide.  If  pure 
carbon  could  be  completely  burned  with  an  amount  of  air  that 
contains  oxygen  just  sufficient  for  the  conversion  of  the  carbon 
to  carbon  dioxide,  the  escaping  gases  would  contain  the  same 
amount  of  carbon  dioxide  as  there  is  oxygen  in  the  air,  namely, 
about  21  per  cent.  The  combustible  matter  in  commercial  fuels 
does  not,  however,  consist  entirely  of  pure  carbon,  and  con- 
sequently the  theoretical  amount  of  carbon  dioxide  that  would 
be  formed  in  their  complete  combustion  will  always  lie  below 
21  per  cent.  If  the  attempt  should  be  made  in  actual  practice 
to  cut  down  the  air  supply  to  the  amount  theoretically  needed 
for  the  combustion  of  the  fuel,  incomplete  combustion  would 
result.  The  amount  of  air  admitted  to  the  fuel  is,  in  proper 
firing,  from  one  and  a  half  to  two  times  that  theoretically  neces- 
sary, with  the  result  that  the  percentage  of  carbon  dioxide  in  the 
flue  gas  will  range  from  about  nine  to  fourteen  per  cent.  With 
careless  firing  or  faulty  construction  of  the  furnace  the  per  cent 

295 


296  GAS  ANALYSIS 

of  carbon  dioxide  in  the  flue  gas  will  fall  below  the  above  amount 
and  the  per  cent  of  oxygen  in  the  escaping  gases  will  correspond- 
ingly rise.  The  greater  the  excess  of  air  admitted  to  the  furnace 
the  larger  will  be  the  amount  of  heat  carried  off  through  the  flue 
by  the  gases. 

In  the  analysis  of  flue  gas,  it  is  at  times  sufficient  to  determine 
merely  the  carbon  dioxide  in  the  gas  mixture.  Usually,  how- 
ever, as  in  a  boiler  test,  it  is  necessary  to  determine  both  carbon 
dioxide  and  oxygen  (and  also  carbon  monoxide  if  present,  al- 
though this  is  rarely  the  case). 

Sampling  of  Flue  Gas.  —  If  the  operator  wishes  merely  to 
ascertain  the  percentages  of  these  three  gases  in  the  flue  gases  at 
certain  intervals,  the  gases  from  the  fire  may  be  drawn  by  a 
bottle  aspirator  through  a  tube  provided  with  a  T-tube  (see 
Fig.  7)  to  which  a  gas  burette  is  attached  in  the  manner  shown. 
Any  other  aspirating  device  may  of  course  be  employed  in  place 
of  the  bottle  aspirator.  It  is  inadmissible  to  collect  or  store  over 
water  any  gas  mixture  containing  carbon  dioxide  if,  in  the  de- 
termination of  that  gas,  results  of  more  than  approximate  ac- 
curacy are  desired.  The  small  bottle  E  contains  a  little  water 
which  serves  to  wash  the  flue  gases  and  to  indicate  their  speed  of 
flow.  Before  a  sample  of  the  flue  gases  is  drawn  off  in  the 
Hempel  burette,  the  pinchcocks  d  and  /  are  opened  and  the 
level-tube  is  raised  until  the  confining  liquid  stands  at  c.  In 
drawing  off  the  sample  for  analysis,  d  and  /  are  opened  and  the 
level- tube  is  slowly  lowered  until  slightly  more  than  100  cc.  of 
gas  has  been  drawn  into  the  burette.  The  two  pinchcocks  are 
then  closed  and  the  rubber  tube  at  the  top  of  the  burette  is 
slipped  off  the  lower  end  of  the  glass  tube  e.  If  only  approxi- 
mate results  are  required,  water  may  be  used  as  the  confining 
liquid  in  the  burette.  For  more  accurate  work  mercury  should 
be  employed. 

If  an  average  sample  of  the  flue  gases  covering  a  period  of 
several  hours  is  desired,  the  sampling  tube  of  Huntly  (see  p.  5) 
should  be  employed  and  the  sample  collected  over  mercury. 


FLUE   GAS  ANALYSIS  297 

Although  Huntly  gives  no  description  of  the  method  to  be  fol- 
lowed in  transferring  the  gas  from  the  sample  tube  to  a  Hempel 
gas  burette,  it  is  obvious  that  this  may  easily  and  accurately  be 
done  in  the  following  manner: 

Invert  the  tube  and  fasten  it  in  a  clamp.  Connect  a  mercury 
level-bulb  with  the  capillary  tube  A  by  a  piece  of  rubber  tubing 
about  40  cm.  long.  Turn  the  stopcock  H  so  that  A  communi- 
cates with  the  side  capillary  tube  B,  thus  driving  all  air  out  of  A. 
Connect  the  capillary  tube  F  with  the  capillary  connecting  tube 
of  the  burette  by  a  short  piece  of  rubber  tubing  in  the  usual 
manner,  and  turn  the  stopcock  K  so  that  F  opens  into  E.  Open 
the  pinchcock  of  the  burette,  raise  the  level-tube  and  in  this  man- 
ner fill  F  with  mercury.  Upon  now  turning  the  stopcock  H  and 
K  to  such  positions  that  A  and  F  communicate  with  C,  and 
lowering  the  level-tube  of  the  burette,  the  gas  sample  will  be 
drawn  over  into  the  burette  without  possibility  of  admixture 
with  air. 

Analysis  of  Flue  Gas.  —  If  the  sample  of  flue  gas  is  taken  in 
the  neighborhood  of  the  laboratory,  the  analysis  may  rapidly 
and  accurately  be  made  either  with  the  form  of  Orsat  apparatus 
devised  by  the  author  and  described  on  p.  85,  or  with  the  ap- 
paratus of  Hempel.  If  the  latter  is  used,  a  sample  of  100  cc.  is 
measured  off  in  a  Hempel  burette  in  the  manner  described  on 
p.  59.  The  three  gases,  carbon  dioxide,  oxygen  and  carbon 
monoxide,  are  then  absorbed  in  the  order  given,  the  decrease  of 
volume  in  cubic  centimeters  in  each  case  giving  directly  the 
percentage  of  the  constituent  in  the  flue. gas. 

Carbon  dioxide  is  absorbed  in  a  Hempel  simple  gas  pipette 
for  solid  reagents  that  is  filled  with  a  concentrated  solution  of 
potassium  hydroxide  (see  p.  225).  The  pipette  is  connected 
with  the  burette  in  the  manner  that  has  already  been  described 
in  detail  on  p.  61  and  the  complete  removal  of  the  carbon 
dioxide  is  accomplished  by  passing  the  gas  mixture  into  the 
pipette,  allowing  it  to  remain  there  for  a  moment  and  then  draw- 
ing it  back  into  the  burette.  If  water  is  being  used  as  the  con- 


298  GAS   ANALYSIS 

fining  liquid  in  the  burette,  it  is  allowed  to  run  down  for  one 
minute  and  the  residual  gas  volume  is  then  read  off,  the  diminu- 
tion in  volume  being  equal  to  the  per  cent  of  carbon  dioxide  in 
the  flue  gas.  For  the  removal  of  oxygen  a  pipette  containing 
phosphorus  (see  p.  164),  alkaline  pyrogallol  (see  p.  160)  or  sodium 
hyposulphite  (see  p.  168)  may  be  employed;  the  manipula- 
tion described  under  these  various  reagents  should  be  carefully 
followed  so  that  the  complete  removal  of  all  of  the  oxygen  in  the 
gas  mixture  may  be  insured.  In  the  analysis  of  flue  gas  with  the 
older  or,  indeed,  with  some  of  the  later  modifications  of  the 
Orsat  apparatus,  oxygen  is  not  entirely  removed.  Since  this  gas 
is  absorbed  by  cuprous  chloride  which  is  next  used  for  the  deter- 
mination of  any  carbon  monoxide  that  may  be  present,  a  diminu- 
tion in  volume  resulting  from  the  absorption  of  oxygen  by  the 
cuprous  chloride  would  naturally  be  ascribed  to  carbon  monoxide 
in  the  gas  mixture.  This  is  a  frequent  cause  of  error  in  the 
analysis  and  in  the  calculations  that  are  based  upon  it. 

After  the  oxygen  has  been  absorbed,  a  double  gas  pipette  con- 
taining ammoniacal  cuprous  chloride  (see  p.  232)  is  connected 
with  the  burette,  the  residual  gas  is  passed  over  into  the  pipette 
and  the  absorption  of  carbon  monoxide  is  effected  by  gently 
shaking  the  pipette  backward  and  forward  without  disconnect- 
ing it  during  a  period  of  three  minutes.  There  will  usually  be  no 
diminution  in  volume  after  this  treatment,  for  flue  gas  rarely 
contains  carbon  monoxide.  It  is  true  that  many  analyses  show 
an  appreciable  amount  of  this  constituent  in  the  gases  formed 
in  combustion,  but  in  the  experience  of  the  author,  this  is  due 
in  the  great  majority  of  cases  to  the  incomplete  removal  of 
oxygen  referred  to  in  the  preceding  paragraph. 

If  the  Orsat-Dennis  apparatus  is  employed,  the  absorption 
pipette  next  to  the  burette  is  filled  with  a  solution  of  potassium 
hydroxide,  the  next  pipette  with  a  solution  of  sodium  hyposul- 
phite or  of  alkaline  pyrogallol  and  the  third  pipette  with  an 
ammoniacal  solution  of  cuprous  chloride.  Carbon  dioxide,  oxy- 
gen and  carbon  monoxide  are  then  absorbed  by  the  three 


FLUE   GAS  ANALYSIS  299 

reagents  in  the  order  given.  The  manipulation  of  the  apparatus 
is  described  on  p.  87. 

Any  sulphur  dioxide  that  is  present  in  the  flue  gas  will  be 
absorbed  by  potassium  hydroxide  in  the  determination  of  carbon 
dioxide.  If  it  is  desired  to  determine  the  amount  of  sulphur 
dioxide  present,  a  fairly  large  sample  of  the  gas  should  be  drawn 
directly  from  the  flue  through  a  tube  containing  a  wad  of  cotton 
to  stop  the  dust,  then  through  a  gas  washing  bottle  containing 
a  measured  volume  of  a  standard  iodine  solution  and  finally 
through  a  gas  meter  for  measurement.  Full  details  of  this 
method  will  be  found  on  p.  274. 

If  the  plant  that  is  being  tested  is  at  a  considerable  distance 
from  the  laboratory,  it  is  frequently  more  convenient  to  make  the 
analysis  of  flue  gas  on  the  spot  than  to  transport  the  gas  sample 
to  the  laboratory.  In  such  case  the  portable  Hempel  apparatus 
described  on  p.  69  or  the  Orsat-Dennis  apparatus  may  be 
employed  with  equally  good  results. 

Automatic  Flue  Gas  Analysis.  —  The  character  and  com- 
pleteness of  the  combustion  in  a  furnace  or  other  heating  appa- 
ratus may,  to  a  considerable  degree,  be  judged  by  the  percentage 
of  carbon  dioxide  in  the  gases  escaping  through  the  flue.  This 
fact  has  led  to  the  invention  of  a  number  of  devices  for  automat- 
ically and  continuously  determining  carbon  dioxide. 

Some  of  these  instruments,  those  that  are  based  upon  the 
determination  of  the  specific  gravity  of  the  flue  gas,  render  it 
possible  to  read  off  the  per  cent  of  carbon  dioxide  at  any  time, 
but  do  not  record  the  results.  The  gas  balance  of  Lux,  the 
dasymeter  of  Siegert  and  Diirr  and  the  econometer  of  Arndt  are 
instruments  of  this  type.  It  is  reported  that  they  are  no  longer 
used  in  practice.  The  apparatus  of  Krell-Schultze  which  is 
based  on  this  principle  has  met  with  favor  in  certain  quarters. 

The  Carbon  Dioxide  Recorder.  —  Another  form  of  appara- 
tus is  that  in  which  carbon  dioxide  in  the  flue  gas  is  absorbed, 
and  the  gas  volume  after  the  absorption  is  automatically  re- 
corded. As  an  example  of  instruments  of  this  form  the  Pre- 


300 


GAS  ANALYSIS 


FIG.  89 

cision  Simmance-Abady  carbon  dioxide  recorder  is   here   de- 
scribed.   A  diagram  of  the  apparatus  is  shown  in  Fig.  89.    a  is 


FLUE   GAS  ANALYSIS  '301 

the  siphon  tank  that  contains  the  float  b;  dd  is  the  extractor 
tank  and  bell;  j[/  is  the  recorder  tank  with  counterbalanced  bell. 
A  small  stream  of  water  flows  in  constantly  through  x  and 
enters  the  reservoir  k  which  is  provided  with  an  overflow  pipe  oo. 
The  water  flows  from  the  reservoir  k  into  the  siphon  tank  a 
through  the  hollow  valve  stem  e.  As  the  water  enters  a  the 
float  b  is  raised,  and  the  bell  d,  which  is  connected  with  b  by 
means  of  the  chain  cc,  falls.  When  the  float  b  rises  to  the  top 
of  the  siphon  tank  it  strikes  the  valve  stem  e,  trips  the  valve 
and  momentarily  flushes  the  siphon  tank,  the  water  flowing  out 
of  a  through  the  tube  g.  This  causes  the  weighted  float  b  to  fall ; 
as  it  does  so  it  lifts  the  extractor  bell  d  and  thus  draws  into  d 
through  the  pipe  p  and  the  three-way  cock  h  a  sample  of  flue  gas. 

The  water  that  passes  through  the  siphon  tube  g  falls  into  the 
small  pan  below  g  which  then  drops,  thereby  raising  the  counter- 
weight q  and  closing  the  valve  h.  This  pan  is  automatically 
emptied  in  time  to  allow  the  valve  h  to  open  again  after  the 
proper  interval. 

In  the  meantime  water  has  been  flowing  into  the  siphon  tank 
a  thus  raising  the  float  b  and  lowering  the  extractor  bell  d.  As 
the  bell  sinks,  the  flue  gas  that  it  contains  is  gradually  brought 
under  pressure  and  is  forced  down  through  the  pipe  that  con- 
nects with  d,  and  through  a  solution  of  potassium  hydroxide 
contained  in  the  reservoir  m.  The  carbon  dioxide  in  the  flue  gas 
is  here  absorbed  and  the  residual  gas  passes  upward  into  the 
recorder  tankj  and  raises  the  bell  in  that  tank.  Attached  to  the 
side  of  this  bell  j  is  a  scale  n  that  is  graduated  from  100  %  at  the 
bottom  to  zero  per  cent  at  the  top.  The  capacity  of  the  bell  of 
the  extractor  tank  d  is  so  chosen  that  when  air  that  is  practically 
free  from  carbon  dioxide  is  passed  through  the  apparatus,  the 
recorder  bell  j  rises  to  the  zero  point  on  the  scale.  When  flue 
gas  is  passed  through  the  apparatus,  the  same  volume  of  gas  is 
collected  in  the  bell  d,  but  on  passage  through  the  solution  of 
potassium  hydroxide  the  carbon  dioxide  in  this  mixture  is 
absorbed,  with  a  consequent  reduction  in  the  volume  of  the  gas 


302 


GAS  ANALYSIS 


escaping  into  j.  The  height  to  which  j  rises,  and  consequently 
the  percentage  of  carbon  dioxide  in  the  gas  mixture  is  auto- 
matically recorded.  The  gas  in  j  is  then  discharged  into  the 
outer  air  and  the  fresh  sample  of  gas  passes  into  it  from  m. 

To  insure  constant 
flow  of  fresh  flue  gas 
into  the  apparatus,  the 
inlet  water  tube  at  x  is 
caused  to  act  as  an  in- 
jector or  aspirator,  and 
is  connected  with  p  by 
a  branch  pipe  that  rises 
and  is  joined  to  the  as- 
pirator by  the  side  arm 
pi.  This  serves  to  con- 
tinuously exhaust  the 
pipes  that  connect  the 
recorder  to  the  boilers, 
which  insures  that  the 
successive  samples  of 
gas  that  are  analyzed 
are  from  the  boiler  flue 
and  are  not  stagnant 
gases  from  the  con- 
necting pipes.  Fig.  90 
shows  this  recorder 
mounted  and  ready  for 
use. 

The  Autolysator.  - 
Instruments      of      the 
FIG.  90  above    type   are   open 

to   the  objection   that 

the  analyses  are  separated  by  intervals  of  several  minutes, 
which  renders  it  impossible  to  read  the  carbon  dioxide  con- 
tent of  the  flue  gas  at  any  desired  moment.  This  difficulty  is 


FLUE   GAS  ANALYSIS 


303 


overcome  by  such  an  apparatus  as  the  Autolysator  of  Strache, 
Johoda  and  Genzken.1  .. 

This  instrument  renders  it  possible  to  read  off,  at  any  moment, 
the  per  cent  of  carbon  dioxide  then  present  in  the  flue  gas,  and 
it  also  furnishes  a  continuous  record  of  the  percentage  of  this 
gas.  The  essential  parts  of  the  device  are  shown  in  Fig.  91.  K 
is  a  capillary  tube  the  ends  of  which  communicate  with  the 
differential  manometer  M .  One  end  of  K  is  connected  with  the 
regulating  valve  A  which  in  turn  is  joined  to  a  water  suction 
pump. 


FIG.  91 

The  passage  of  the  gas  through  the  capillary  K  is  dependent 
upon  the  difference  in  pressure  shown  upon  the  manometer  M . 
If  the  volume  of  gas  is  kept  constant  by.a  proper  adjustment  of 
the  valve  A  the  volume  of  gas  passing  through  K  is  also  constant. 
The  specific  gravity  of  the  gas  has  no  influence  upon  the  speed 
of  flow  through  the  long  capillary  tube.  The  constant  volume 
of  gas  passing  through  K  is  drawn  through  a  second  capillary  / 
the  two  ends  of  which  are  joined  to  the  manometer  N. 

Between  the  two  capillary  tubes  are  introduced  the  absorp- 
tion vessels  B  and  C  which  serve  to  free  the  gas  that  is  passed 

1 Z.  /.  chemische  Apparatenkunde,  2  (1907),  57. 


304  GAS  ANALYSIS 

through  J  from  the  constituent  that  is  to  be  determined. 
The  gas  mixture  under  examination  enters  the  apparatus 
at  D. 

It  is  apparent  that  if  no  gas  is  absorbed  when  the  mixture 
passes  through  B  and  C  the  same  amount  of  gas  will  pass  through 
the  capillary  /  in  a  unit  of  time  as  flows  through  the  capillary  K. 
If  the  two  capillaries  are  exactly  the  same  diameter  and  length, 
the  difference  in  pressure  in  TV  will  be  exactly  the  same  as  that 
shown  by  M.  If,  on  the  other  hand,  the  absorption  vessels  B 
and  C  remove  a  constituent  of  the  gas  mixture,  then  a  larger 
volume  of  gas  must  pass  through  the  capillary  /  in  a  unit  of 
time  than  through  the  capillary  K.  If,  now,  with  the  aid  of  the 
regulating  valve  A  the  reading  of  the  manometer  M  and  conse- 
quently the  gas  volume  flowing  through  K  be  kept  constant, 
the  amount  of  gas  that  will  pass  through  /  will  increase  in 
proportion  to  the  percentage  of  absorbable  constituents  that  it 
contains.  This  will  increase  the  difference  in  level  of  the  liquid 
in  the  two  arms  of  the  manometer  N  and  this  difference  shows 
directly  the  percentage  of  the  absorbed  constituent  in  the  gas 
mixture.  By  means  of  an  empirical  scale  attached  to  N  the 
percentage  in  the  gas  mixture  of  the  gas  that  is  being  absorbed 
in  B  and  C  may  be  read  off  at  any  moment.  The  apparatus  is 
further  provided  with  an  automatic  registering  device  which 
gives  a  continuous  record  of  the  percentage  of  absorbed  gas. 
This  form  of  autolysator  is  manufactured  by  the  Vereinigte 
Fabriken  fur  Laboratoriumsbedarf,  Berlin. 

The  Gas  Refractometer.  —  Another  interesting  instrument 
for  the  determination  of  a  constituent  gas  in  a  mixture  of  gases 
is  the  Gas  Refractometer  designed  by  Haber.1  The  method  is 
based  upon  the  fact,  first  ascertained  by  Dulong,2  that  the 
light-refraction  of  gases  may  be  determined  with  exactness  by 
means  of  a  gas  prism  and  telescope;  and  upon  the  law  of  Biot  and 

1  Vortrag  auf  der  Hauptversammlung  des  Vereins  deutscher  Chemiker,  Nurnberg, 
June  8,  1906.    Also  in  Zeit.f.  angew.  Chem.,  19  (1906),  1418. 

2  Ann.  de  chim.  et  de  phys.,  31  (1826),  154. 


FLUE  GAS  ANALYSIS  305 

Arago  1  that  the  light-refraction  of  a  gas  mixture  may  be  cal- 
culated in  simple  manner  from  the  refraction  of  the  several 
constituents  and  their  partial  pressures. 

In  other  words,  if  the  index  of  refraction,  less  one,  is  termed 
the  refractive  power,  the  total  refractive  power  of  a  gas  mixture 
is  equal  to  the  sum  of  the  refractive  powers  of  the  constituent 
gases  in  the  same  manner  as  the  total  pressure  of  a  gas  mixture 
is  equal  to  the  sum  of  the  partial  pressures  of  the  several  gases 
that  are  present. 

To  determine  the  percentage  of  a  gas  in  a  mixture  with  the 
aid  of  the  gas  refractometer,  the  refraction  of  the  mixture  is 
first  measured,  and  then  the  refraction  of  the  residue  after  the 
removal  of  the  constituent  in  question.  Or  if  it  is  desired  to 
ascertain  the  amount  of  a  gas  that  has  been  added  to  a  mixture, 
as  in  the  carburetting  of  illuminating  gas,  the  refraction  before 
and  after  the  addition  of  the  gas  is  measured. 

The  refractometer  has  been  successfully  employed  in  the 
solution  of  certain  special  problems  in  technical  practice.  It  is 
manufactured  by  the  firm  Carl  Zeiss  in  Jena,  Germany. 

L M em.  de  I'Acad.  de  France,  7  (1806),  301. 


CHAPTER  XV 

ILLUMINATING  GAS  — FUEL  GAS 

COAL  GAS  — PINTSCH  GAS  — WATER  GAS  — PRODUCER  GAS 
BLAST-FURNACE  GAS  — NATURAL  GAS 

The  gas  mixtures  that  fall  under  the  above  heading  show 
great  differences  in  composition,  but  they  are  here  grouped 
together  because  the  methods  employed  for  their  analysis  and 
the  sequence  of  the  several  determinations  are  closely  similar 
and,  in  many  cases,  identical. 

Probably  the  most  complex  of  these  gas  mixtures  is  that 
which  results  from  the  destructive  distillation  of  coal,  a  product 
termed  coal  gas.  A  detailed  description  of  the  methods  em- 
ployed in  the  examination  of  this  gas  is  given  in  the  following 
pages,  and  will  be  found  to  include  practically  all  of  the  points 
involved  in  the  analysis  of  the  other  gas  mixtures  enumerated 
at  the  head  of  this  chapter. 

COAL   GAS 

Although  the  quantitative  composition  of  coal  gas  varies  with 
the  methods  employed  in  its  manufacture  and  with  the  nature 
of  the  coal,  the  constituents  of  the  product  are  nearly  the  same 
in  every  case.  The  washed  gas  contains  carbon  dioxide,  carbon 
monoxide,  hydrogen,  methane,  heavy  hydrocarbons  (illumi- 
nants),  vapors  of  other  hydrocarbons  such  as  benzene  and 
naphthalene,  gaseous  compounds  of  sulphur,  water  vapor,  ni- 
trogen, oxygen,  and  sometimes  cyanogen  or  hydrogen  cyanide. 
The  unwashed  gas  contains  ammonia  and  uncondensed  tar,  in 
addition  to  the  above  ingredients. 

The  complete  examination  of  coal  gas  comprises:  — 
i.  The  determination  of  the  illuminating  power  of  the  gas; 

306 


ILLUMINATING   GAS  —  FUEL   GAS  307 

2.  The   determination   of   the   specific  gravity  of  the  gas; 

3.  The  gas  volumetric  determination  of  the  principal  con- 
stituents of  the  gas  mixture; 

4.  The  determination  of  naphthalene; 

5.  The  determination  of  the  total  sulphur  in  the  gas; 

6.  The  determination  of  the  total  cyanogen  in  the  gas; 

7.  The  determination  of  the  heating  value  of  the  gas  (see 
Chapter  XVI). 

i.  The  Determination  of  the  Illuminating  Power  of  Coal  Gas 

In  the  measurement  of  the  intensity  of  sources  of  light  two 
general  methods  are  employed,  the  direct-comparison  method 
and  the  substitution  method.  In  the  first,  the  light  whose 
intensity  is  to  be  measured  is  placed  on  one  side  of  the  photo- 
metric apparatus  and  the  standard  light  on  the  other  side  and 
the  two  are  directly  compared.  In  the  second,  a  light  of  con- 
venient intensity  is  compared  with  the  standard;  the  standard 
is  then  removed  and  the  light  whose  intensity  is  to  be  compared 
is  then  put  in  its  place.  The  intensity  of  the  last  light  in  the 
terms  of  the  standard  is  then  computed. 

While  the  substitution  method  is  in  general  superior  to  that 
of  direct  comparison  the  latter  is  usually  employed  in  the  in- 
dustrial measurement  of  the  illuminating  power  of  gases. 

The  most  satisfactory  primary  standards  are  the  sperm 
candle,  the  pentane  lamp,  the  Hefner  amylacetate  lamp  and  the 
carbon-filament  incandescent  lamp.1  Many  forms  of  photom- 
eter have  been  devised.  Full  details  concerning  their  construc- 
tion and  use  may  be  found  in  Praktische  Photometric  by  Dr. 
Emil  Liebenthal  (1907)  and  in  Photometric  Units  and  Standards 
by  E.  B.  Rosa  (see  note). 

Of  the  direct  comparison  instruments,  that  designed  by  Bunsen 
is  widely  used  and  gives  quite  satisfactory  results.  The  instru- 

1  A  discussion  of  these  standards  will  be  found  in  the  lecture  of  Rosa  upon  pho- 
tometric units  and  standards  published  in  Lectures  on  Illuminating  Engineering,  The 
Johns  Hopkins  Press,  1911. 


308  GAS  ANALYSIS 

ment  is  constructed  on  the  following  principle.  If  a  spot  upon 
a  screen  of  white  paper  is  rendered  translucent  by  pressing 
grease  or  wax  into  the  paper,  and  the  screen  is  then  held  between 
two  sources  of  light,  the  grease  spot  will  appear  darker  than  the 
surrounding  paper  when  the  screen  is  viewed  from  the  side  on 
which  the  stronger  light  falls.  If  the  illumination  on  the  further 
side  of  the  paper  is  the  stronger,  the  spot  will  appear  to  the  eye 
to  be  lighter  than  the  rest  of  the  screen.  If  the  screen  is  moved 
to  such  position  between  the  two  sources  of  light  that  the  in- 
tensity of  light  falling  upon  each  side  of  it  is  the  same,  the  spot 
will  disappear.  The  distance  from  the  screen  to  each  of  the  two 
lights  is  now  measured.  Since  the  intensities  of  the  two  flames 
are  to  each  other  as  the  squares  of  the  distances  of  the  flames 
from  the  screen,  the  candle  power  of  one  flame  in  terms  of  the 
other  may  be  computed  according  to  the  formula 


in  which  7  is  the  candle  power  of  the  light  of  known  intensity 


mi 

LWJ 


o 
FIG.  92 

and  d  the  distance  of  this  light  from  the  screen,  and  /'  is  the 
candle  power  of  the  light  being  measured  and  d'  its  distance  from 
the  screen. 

The  construction  of  the  Bunsen  photometer  is  shown  in 
Fig.  92. 

LI  and  L2  are  the  two  sources  of  light  under  comparison  and 


ILLUMINATING   GAS  —  FUEL  GAS  309 

5*  the  screen  of  paper  on  which  is  the  grease  spot.  To  enable  the 
operator  to  see  both  sides  of  the  screen  simultaneously,  the 
Riidorff  mirrors  M \  and  MI,  each  placed  at  an  angle  of  70°  with 
the  plane  of  the  screen,  are  almost  universally  employed.  Upon 
looking  through  the  opening  0  the  eye  sees  the  two  images  of 
the  disk. 

In  determining  the  intensity  of  a  source  of  light  Z,2,  in  terms  of 
LI,  the  photometer  screen  is  moved  to  the  right  or  left  until  the 
contrast  between  the  greased  and  ungreased  portions  of  the 
screen  is  the  same  on  one  side  as  on  the  other.  The  distances 
from  the  screen  to  the  two  sources  of  light  are  then  read  off, 
and  the  intensity  of  Lz  computed  by  means  of  the  formula  given 
above. 

2.  The  Determination  of  the  Specific  Gravity  of  Coal  Gas 

The  specific  gravity  of  coal  gas  is  usually  determined  by  meas- 
uring its  time  of  escape  through  a  small  opening.  Methods 
that  may  be  employed  for  this  purpose  are  described  on  p.  44. 

j.  The  Gas-Volumetric  Analysis  of  Coal  Gas 

The  volumetric  analysis  of  coal  gas  comprises  the  determina- 
tion of  such  constituents  as  are  present  in  amounts  sufficient  to 
permit  of  their  accurate  determination  in  a  sample  of  not  more 
than  100  cubic  centimeters. 

These  gases  usually  are:  — 

1.  Carbon  dioxide, 

2.  Benzene, 

3.  Other  heavy  hydrocarbons,  chiefly  ethylene, 

4.  Oxygen, 

5.  Carbon  monoxide, 

6.  Hydrogen, 

7.  Methane  (and  sometimes  ethane), 

8.  Nitrogen. 

Inasmuch  as  methods  for  the  determination  of  these  various 
gases  have  already  been  described  in  Chapter  XIII,  there  will 


310  GAS  ANALYSIS 

here  be  given  only  a  description  of  the  successive  steps  em- 
ployed in  a  complete  volumetric  analysis  of  coal  gas,  together 
with  such  details  of  the  manipulation  as  have  not  previously 
been  discussed. 

The  Determination  of  the  Absorbable  Gases.  Appara- 
tus. —  In  the  opinion  of  the  author,  the  best  form  of  apparatus 
for  the  rapid  and  accurate  determination  of  the  absorbable  con- 
stituents of  coal  gas,  numbers  i  to  5  inclusive  in  the  above  list, 
is  that  of  Hempel.  The  Orsat-Dennis  apparatus  gives  equally 
good  results,  but  if  constructed  with  the  six  absorption  pipettes 
that  are  needed  for  the  removal  of  the  five  absorbable  gases,  it 
becomes  so  unwieldy  that  it  cannot  be  recommended  for  this 
purpose. 

For  usual  technical  practice,  a  Hempel  gas  burette  without 
water  jacket  may  be  employed,  although  somewhat  more  ac- 
curate results  can  be  obtained  with  the  use  of  a  water  mantle 
around  the  burette.  If  the  room  in  which  the  analysis  is  carried 
on  undergoes  fluctuations  of  temperature,  a  water-jacketed 
burette  should  be  used  in  all  cases.  The  accuracy  of  the  analysis 
is  of  course  increased  by  the  use  of  mercury  as  the  confining 
liquid  in  the  burette,  but  the  differences  between  the  results 
obtained  over  mercury  and  over  water  are  usually  not  great 
enough  to  warrant  the  employment  of  mercury  in  technical 
practice. 

Manipulation.  —  Clean  the  burette  and  level- tube  (Fig.  33) 
and  see  that  the  rubber  tube  on  the  upper  end  of  the  burette  is 
in  good  condition  and  is  securely  fastened  in  place  by  the  wire 
ligature.  Place  an  amount  of  water  sufficient  for  the  filling  of 
the  burette  and  level-tube  in  a  flask,  and  saturate  it  with  the 
coal  gas  that  is  to  be  analyzed  (see  p.  59).  Fill  the  burette 
and  level-tube  with  this  water  in  the  manner  described  on 

P-  59- 

Connect  a  glass  tube  to  the  gasometer  or  pipe  containing  the 
coal  gas  by  means  of  a  short  piece  of  rubber  tubing.  Pass  the 
gas  through  this  tube  until  all  air  has  been  expelled,  insert  the 


ILLUMINATING   GAS  —  FUEL   GAS  311 

end  of  it  into  the  rubber  tube  at  the  top  of  the  burette,  and  draw 
into  the  burette  somewhat  more  than  100  cc.  of  the  gas.  Close 
the  pinchcock  at  the  top  of  the  burette,  disconnect  the  glass  tube, 
and  after  the  water  in  the  burette  has  run  down  for  one  minute 
measure  off  a  sample  of  exactly  100  cc.  at  atmospheric  pressure 
in  the  manner  described  on  p.  59.  Verify  the  accuracy  of 
this  measurement  by  bringing  the  water  levels  in  the  burette 
and  level-tube  to  the  same  height  and  noting  whether  the 
meniscus  in  the  burette  stands  exactly  at  the  100  cc.  mark. 

Carbon  Dioxide.  —  Place  a  wooden  pipette  stand  at  the  side 
of  the  burette,  and,  upon  the  stand,  a  Hempel  gas  pipette  for 
the  absorption  of  carbon  dioxide  (p.  225).  Connect  the  pipette 
with  the  burette  by  either  of  the  procedures  described  on 
pp.  6 1  and  64.  Where  a  number  of  analyses  are  to  be  made 
one  after  another,  the  second  method  of  connecting  the  pipettes 
with  the  burette,  described  on  p.  64,  in  which  a  pinchcock  is  placed 
upon  the  rubber  tube  of  the  pipette,  and  the  solution  in  the 
pipette  is  driven  over  to  the  far  bend  of  the  connecting  capillary 
tube  and  is  held  there  by  closing  the  pinchcock  on  the  pipette, 
will  be  found  to  add  much  to  the  convenience  of  the  manipu- 
lation and  to  the  rapidity  of  the  analysis.  Employ  this  ma- 
nipulation in  connecting  other  pipettes  with  the  burette  unless 
there  is  a  reason  for  not  driving  the  reagent  up  into  the  con- 
necting capillary  tube,  which  is  the  case  with  fuming  sulphuric 
acid. 

Open  the  pinchcock  at  the  top  of  the  burette,  and  pass  the 
gas  sample  into  the  pipette,  allowing  the  water  from  the  burette 
to  follow  to  the  first  bend  of  the  capillary  tube  of  the  pipette. 
After  the  gas  has  stood  for  thirty  seconds  in  the  pipette,  draw 
it  back  into  the  burette  by  lowering  the  level-tube,  and  bring 
the  solution  of  potassium  hydroxide  to  the  same  point  in  the 
connecting  capillary  at  which  it  stood  when  the  pipette  and 
burette  were  first  connected.  Disconnect  the  pipette,  allow  the 
water  in  the  burette  to  run  down  for  one  minute,  bring  the  sur- 
face of  the  water  in  the  level-tube  to  the  same  height  as  that  in 


312  GAS  ANALYSIS 

the  burette  and  read  the  volume  of  the  residual  gas.  The  dim- 
inution in  volume  measured  in  cubic  centimeters  gives  directly 
the  percentage  of  carbon  dioxide  in  the  coal  gas. 

Benzene.  —  Replace  the  potassium  hydroxide  pipette  by  a 
double  pipette  for  solid  reagents  (p.  58)  that  is  charged  with  a 
solution  of  ammonia  nickel  cyanide  (p.  256).  Connect  the  bu- 
rette with  this  pipette  in  the  manner  employed  above  and  pass 
the  gas  repeatedly  back  and  forth  between  the  burette  and 
pipette  for  a  period  of  three  minutes.  Pass  the  gas  into  the 
burette,  close  the  pinchcock  at  the  top  of  the  burette,  and  re- 
place the  pipette  containing  ammonia  nickel  cyanide  by  a 
double  pipette  for  solid  reagents  that  is  charged  with  a  five  per 
cent  solution  of  sulphuric  acid  (p.  257).  Pass  the  gas  back  and 
forth  about  two  minutes  to  remove  ammonia.1  Then  draw  the 
gas  into  the  burette,  close  the  pinchcock,  allow  the  water  in  the 
burette  to  run  down  for  one  minute  as  usual,  and  read  the 
volume  of  the  gas.  The  difference  between  this  volume  and  that 
remaining  after  the  absorption  of  the  carbon  dioxide,  measured 
in  cubic  centimeters,  gives  the  percentage  of  benzene  in  the 
gas. 

Other  Heavy  Hydrocarbons.  —  Connect  the  burette  by 
means  of  a  dry  capillary  tube  with  a  pipette  containing  fuming 
sulphuric  acid,  making  the  connection  and  effecting  the  absorp- 
tion in  the  manner  described  on  p.  247. 

Draw  the  gas  back  into  the  burette  to  such  point  that  the  acid 
stands  at  the  original  height  in  the  capillary  tube  of  the  pipette. 
Close  the  pinchcock  at  the  top  of  the  burette,  replace  the  sul- 
phuric acid  pipette  by  one  containing  potassium  hydroxide,  and 
pass  the  gas  into  this  pipette  to  remove  sulphur  trioxide  and  sul- 
phur dioxide.  Drive  the  acid  back  into  the  burette,  and  measure 
the  decrease  in  volume  after  the  water  has  run  down  for  the 

1  If  mercury  is  used  in  the  burette  the  small  amount  of  water  that  usually  covers 
its  surface  will  absorb  a  considerable  quantity  of  ammonia  from  the  reagent.  In 
such  case  a  volume  of  dilute  sulphuric  acid  amply  sufficient  to  neutralize  the  am- 
monium hydroxide  thus  formed  should  be  drawn  over  from  the  pipette  into  the  bu- 
rette, and  then  driven  back  into  the  pipette. 


ILLUMINATING   GAS  —  FUEL  GAS  313 

usual  one  minute.  The  difference  between  this  and  the  last 
reading  gives  the  percentage  of  heavy  hydrocarbons  other  than 
benzene. 

Oxygen.  —  Connect  the  burette  with  the  pipette  contain- 
ing phosphorus  or  alkaline  pyrogallol  or  sodium  hyposulphite, 
and  remove  the  oxygen  in  the  manner  described  in  Chapter  XIII 
for  the  reagent  that  is  employed.  The  diminution  in  volume 
resulting  from  this  absorption  gives  the  percentage  of  oxygen  in 
the  gas. 

Carbon  Monoxide.  —  Join  the  burette  to  a  Hempel  double 
pipette  containing  ammoniacal  or  acid  cuprous  chloride  (see 
p.  232),  drive  the  gas  over  into  the  pipette,  and  hasten  the  ab- 
sorption of  the  carbon  monoxide  by  gently  rocking  the  pipette 
backwards  and  forwards  for  three  minutes  without  disconnect- 
ing it  from  the  burette  (see  p.  63).  Draw  the  gas  back  into 
the  burette,  close  the  pinchcock  of  the  burette,  and  replace  the 
pipette  with  another  pipette  containing  a  solution  of  cuprous 
chloride  that  has  been  but  slightly  used.  Repeat  the  manipula- 
tion and  after  two  minutes  shaking  pass  the  gas  back  into  the 
burette.  Some  ammonia  or  hydrogen  chloride  from  the  reagent 
will  now  be  present  in  the  gas  mixture.  When  water  is  used  as 
the  confining  liquid  in  the  burette,  these  gases  will  be  absorbed 
by  it.  But  when  mercury  is  employed  as  the  confining  liquid 
they  should  be  removed  before  the  gas  is  measured,  the  ammonia 
by  passing  the  gas  into  a  pipette  containing  5%  sulphuric  acid, 
the  hydrogen  chloride  by  passing  the  gas  into  a  pipette  con- 
taining potassium  hydroxide.  Measure  the  residual  volume. 
The  diminution  in  volume  gives  the  per  Cent  of  carbon  monoxide 
in  the  gas. 

Disconnect  the  cuprous  chloride  pipette  and  replace  it  by  a 
simple  pipette  (Fig.  34)  containing  water,  and  pass  the  gas 
residue  from  the  burette  into  this  pipette,  allowing  the  water 
from  the  burette  to  follow  over  to  the  lower  bend  in  the  long 
capillary  tube  of  the  pipette.  Pour  out  the  water  in  the  burette 
and  level-tube,  rinse  out  the  tubes  first  with  dilute  hydrochloric 


314  GAS  ANALYSIS 

acid  and  then  with  distilled  water,  and  fill  them  with  distilled 
water.  Pass  the  gas  back  again  into  the  burette  and  measure  its 
volume. 

If  hydrogen,  methane,  and  nitrogen  are  to  be  simultaneously 
determined  in  the  combustion  pipette  (see  below),  the  gas  residue 
may  be  passed  directly  into  this  pipette  after  the  determination 
of  carbon  monoxide.  The  burette  that  is  used  in  the  combus- 
tion is  filled  with  mercury,  not  with  water. 

Hydrogen,  Methane  (and  Ethane),  and  Nitrogen.  — 
These  gases  may  be  determined  separately  by  the  successive 
removal  of  hydrogen  and  the  paraffins,  or  if  methane  is  the  only 
hydrocarbon  present  they  may  be  determined  simultaneously 
by  a  single  explosion  or  combustion.  If  ethane  is  present  with 
methane,  the  amounts  of  the  two  hydrocarbons  cannot  be  deter- 
mined by  combustion  unless  the  hydrogen  is  first  removed  (see 
Chapter  XI). 

For  the  simultaneous  determination  of  hydrogen,  methane 
and  nitrogen,  and  of  methane,  ethane  and  nitrogen  the  combus- 
tion method  of  Dennis  and  Hopkins  is  to  be  preferred  to  the 
explosion  of  the  residue  with  air  or  oxygen  because  in  the  former 
procedure  the  possibility  of  incomplete  combustion  or  of  the 
formation  of  measurable  amounts  of  oxides  of  nitrogen  is 
avoided,  and  because  further  the  complete  oxidation  of  the  com- 
bustible gases  is  independent  of  the  composition  of  the  gas  mix- 
ture. The  manipulation  of  the  combustion  pipette  for  the  simul- 
taneous determination  of  hydrogen,  methane  and  nitrogen,  and 
the  calculation  of  the  analytical  results  is  described  in  detail  on 
pp.  149  and  244.  If  both  methane  and  ethane  are  present  with 
hydrogen  and  nitrogen  in  the  residue  remaining  after  the  removal 
of  the  absorbable  gases,  the  hydrogen  is  first  removed,  and  the 
methane  and  ethane  are  then  burned  in  the  combustion  pipette, 
the  total  contraction  being  noted,  and  the  volume  of  carbon 
dioxide  formed  being  ascertained. 

The  percentages  of  methane  and  ethane  are  then  calculated 
by  means  of  equations  7  and  8  on  p.  130. 


ILLUMINATING  GAS  —  FUEL  GAS  315 

If  x  represents  methane  and  y  ethane,  then 

C02     =  CH4  +  2  C2H6,  (7) 

and 

T.C.    =2  CH4  +  2^C2H6        (8) 

Subtracting  the  second  equation  from  twice  the  first 
2  CO2  —  T.  C.  -  ijC2H6  or 


C2H6 


3 
Then,  knowing  the  volume  of  ethane, 

CH4  =  C02  —  2  C2H6 

The  successive  determination  of  hydrogen,  methane  (and 
ethane)  and  nitrogen  may  be  accomplished  in  a  variety  of  ways; 
the  hydrogen  is  first  removed,  the  hydrocarbons  are  then 
burned,  and  the  nitrogen  is  calculated  by  difference. 

Of  the  many  methods  for  the  removal  and  determination  of 
hydrogen,  the  most  convenient  and  accurate  are  the  absorption 
with  palladium  black  (see  p.  188),  and  the  fractional  combus- 
tion with  copper  oxide  (see  p.  201).  The  fractional  combus- 
tion with  palladium  asbestos  cannot  be  recommended  for  the 
reasons  set  forth  on  p.  193  to  196.'  The  Hempel  method  of 
fractional  combustion  with  palladium  black  (see  p.  196)  re- 
moves hydrogen  completely,  but  it  is  open  to  the  objection  that 
only  a  small  portion  of  the  combustible  residue  is  used,  with 
consequent  multiplication  of  any  error  that  may  be  made  in  the 
measurements. 

If  the  hydrogen  is  to  be  removed  by  absorption  with  palladium 
black,  the  gas  burette  containing  the  gas  residue  is  connected 
with  the  U-tube  containing  the  palladium  black,  the  amount 
of  air  in  this  U-tube  having  previously  been  ascertained  by  the 
method  described  on  p.  190.  The  hydrogen  is  then  absorbed 
(see  p.  189),  and  the  residual  gas  is  drawn  back  into  the 
burette  and  measured.  The  diminution  in  volume  is  equal  to 


316  GAS  ANALYSIS 

the  hydrogen  in  the  gas  residue  plus  the  oxygen  in  the  air  that 
was  originally  inclosed  in  the  U-tube  when  the  apparatus  was 
put  together.  Subtracting  this  volume  of  oxygen  from  the  total 
contraction  gives  the  hydrogen  in  the  gas. 

If  the  hydrogen  is  to  be  removed  by  fractional  combustion 
with  copper  oxide,  the  apparatus  and  method  described  on 
pp.  201  to  206  is  employed. 

After  hydrogen  has  been  determined  either  by  absorption 
with  palladium  black  or  by  fractional  combustion  with  copper 
oxide,  the  tubes  used  in  these  methods  will  still  contain  some 
of  the  combustible  residue  which  must  be  swept  over  into  the 
burette  with  about  30  cc.  of  nitrogen  gas  from  a  phosphorus 
pipette  before  the  combustion  of  the  hydrocarbons  is  proceeded 
with.  It  is  not  necessary  to  know  the  volume  of  nitrogen  that 
is  hereby  added  to  the  gas  residue,  but  the  total  volume  of  the 
residue  and  the  nitrogen  that  has  been  added  to  it  must  be  ascer- 
tained by  measurement  before  the  combustion  is  made. 

After  the  removal  of  the  hydrogen,  the  determination  of  the 
hydrocarbons  of  the  paraffin  series  is  next  made.  If  methane 
is  the  only  hydrocarbon  present,  the  combustion  may  be  carried 
out  in  a  combustion  pipette  filled  with  water  because  it  is  here 
not  necessary  to  determine  the  volume  of  carbon  dioxide  that 
is  formed  in  the  combustion.  If,  however,  the  residue  con- 
tains both  methane  and  ethane,  the  gas  burette  and  the  com- 
bustion pipette  should  be  filled  with  mercury  because  both 
the  total  contraction  and  the  volume  of  carbon  dioxide  formed 
must  be  ascertained  (see  p.  315).  If  methane  is  the  only  hydro- 
carbon present  the  combustion  is  carried  out  as  follows: 

About  100  cc.  of  oxygen  or  of  air,  if  that  volume  of  air  con- 
tains enough  oxygen  to  insure  complete  combustion,  is  run  into 
the  combustion  pipette,  which  is  then  joined  to  the  burette  con- 
taining the  gas  residue.  The  terminals  of  the  pipette  are  then 
connected  writh  the  source  of  current,  the  current  is  turned  on, 
and  the  spiral  heated  to  dull  redness.  The  gas  residue  is  slowly 
passed  into  the  pipette,  the  current  being  regulated  so  that  the 


ILLUMINATING  GAS  —  FUEL  GAS  317 

spiral  will  not  rise  above  a  dull  red  heat  at  any  time.  When  all 
of  the  gas  has  been  passed  over  into  the  pipette,  the  platinum 
spiral  is  kept  at  dull  redness  for  60  seconds.  The  current  is  then 
turned  off,  the  pipette  is  allowed  to  cool,  and  the  residual  gas  is 
passed  back  into  the  burette.  Without  measuring  the  residual 
gas  volume  at  this  point,  the  combustion  pipette  is  detached, 
and  a  gas  pipette  containing  potassium  hydroxide  is  connected 
with  the  burette.  The  gas  is  passed  over  into  this  pipette  to 
remove  all  carbon  dioxide  and  is  drawn  back  into  the  burette 
and  measured.  When  methane  is  burned,  one  volume  of  the  gas 
unites  with  two  volumes  of  oxygen  to  form  one  volume  of  carbon 
dioxide  and  two  molecules  of  water.  If  the  carbon  dioxide  re- 
sulting from  the  combustion  is  absorbed,  the  diminution  in 
volume  that  results  from  the  combustion  of  one  volume  of 
methane  equals  three  times  the  volume  of  the  gas. 

CH4     -f  2  O2        =  C02        +  2  H2O 
i  vol.       2  vols.         absorbed       liquid 

Consequently  one-third  of  the  total  diminution  observed  in  this 
combustion  equals  the  volume  of  methane  that  is  present  in  the 
gas  residue. 

If  the  residue  contains  both  methane  and  ethane,  the  combus- 
tion is  carried  out  over  mercury,  the  contraction  in  volume  after 
the  combustion  is  measured,  and  the  volume  of  carbon  dioxide 
that  has  been  formed  is  determined  by  absorption  with  potas- 
sium hydroxide.  The  percentage  of  each  of  the  gases  is  then 
calculated  by  the  method  given  on  p.  315. 

Nitrogen.  —  It  has  hitherto  been  customary  in  the  analysis 
of  coal  gas  to  state  that  the  amount  of  nitrogen  in  the  gas  is 
equal  to  the  final  residual  gas  volume  after  the  removal  of  the 
absorbable  constituents  and  the  combustible  gases.  Usually, 
however,  small  amounts  of  air  are  left  in  the  connecting  capil- 
lary tube  when  the  burette  and  pipettes  are  joined  together, 
and  these  minute  air  volumes  will  cause  errors  that,  although 
negligible  in  the  separate  determinations,  have  a  cumulative 


3i8  GAS  ANALYSIS 

effect  of  considerable  magnitude  upon  the  volume  of  residual 
nitrogen.  For  this  reason  it  is  preferable  to  determine  nitrogen 
in  a  separate  sample  of  the  gas. 

This  may  be  done  by  burning  a  sample  of  the  gas  with  an  ex- 
cess of  oxygen,  removing  the  products  of  combustion  by  means 
of  potassium  hydroxide,  absorbing  the  excess  of  oxygen  with  an 
alkaline  solution  of  pyrogallol,  and  measuring  the  residue, 
which  should  be  pure  nitrogen.  The  method  is  carried  out  as 
follows: 

100  cc.  of  pure  oxygen  free  from  combustible  gases,  and  con- 
taining either  no  nitrogen,  or  nitrogen  of  known  amount,  is 
placed  in  the  combustion  pipette,  and  a  measured  amount  of  the 
sample  of  illuminating  gas,  about  50  cc.,  is  passed  from  a  Hempel 
burette  into  the  combustion  pipette  in  the  usual  manner.  After 
combustion  is  complete  the  residue  is  returned  to  the  burette, 
and  carbon  dioxide  and  the  excess  of  oxygen  are  removed  by 
passing  the  gas  residue  successively  into  a  pipette  containing 
potassium  hydroxide  and  one  containing  alkaline  pyrogallol. 
The  residual  gas  is  nitrogen.  Since  a  sample  of  coal  gas  less  than 
100  cc.  is  used  in  this  determination,  the  per  cent  of  nitrogen 
in  the  gas  is  not  equal  to  the  residual  volume,  but  to 

residual  volume  X  100 
volume  of  sample 

4.  The  Determination  of  Naphthalene  in  Coal  Gas 


Naphthalene  is  best  determined  by  absorption  in  picric  acid 
according  to  the  method  described  on  p.  261.  Before  the  gas 
enters  the  absorbent,  however,  it  should  be  freed  from  tar, 
cyanogen,  hydrogen  sulphide  and  ammonia.  This  may  be 
accomplished  1  by  passing  the  gas  mixture  through  three  wash 
bottles  containing  dilute  sulphuric  acid  and  then  through  two 
wash  bottles  containing  a  solution  of  potassium  hydroxide  (the 
authors  do  not  give  the  strength  of  these  reagents),  the  five 

1  Albrecht  and  Muller,  /./.  Gasbeleuchtung,  54  (1911),  592. 


ILLUMINATING  GAS  —  FUEL  GAS  319 

wash  bottles  being  connected  glass  to  glass  by  short  pieces  of 
rubber  tubing  and  being  placed  in  a  drying  oven  heated  to 
about  50°.  From  the  last  washing  bottle  the  gas  passes  through 
two  wash  bottles  containing  picric  acid,  these  bottles  being  out- 
side of  the  oven  and  being  connected  at  their  further  end  with  a 
gas  meter  and  suction  pump. 

5.  The  Determination  of  Total  Sulphur  in  Coal  Gas 

Illuminating  gas  that  is  prepared  by  the  dry  distillation  of 
coal  always  contains  compounds  of  sulphur  such  as  hydrogen 
sulphide  and  carbon  disulphide.  Although  the  greater  part  of 
these  products  is  removed  in  the  purification  of  the  gas  before  it 
is  admitted  to  the  mains,  some  of  the  compounds  are  always 
found  in  the  washed  gas.  These  sulphur  compounds  are  ob- 
jectionable because  of  the  sulphur  dioxide  that  results  from 
their  combustion.  Inasmuch  as  all  of  them  form  sulphur 
dioxide  when  they  are  burned,  the  determination  of  the  total 
sulphur  in  the  gas  is  customarily  required,  and  usually  no 
attempt  is  made  to  determine  the  separate  compounds  of  the 
element  that  are  present. 

The  method  that  is  most  generally  employed  for  the  deter- 
mination of  the  total  sulphur  in  illuminating  gas  consists  in 
burning  the  gas  with  the  aid  of  oxygen  or  air,  converting  the 
resulting  sulphur  dioxide  to  sulphuric  acid,  and  determining 
that  final  product  by  gravimetric  or  volumetric  means.1 

The  two  forms  of  apparatus  most  generally  used  for  this 
determination  are  that  proposed  by  Drehschmidt 2  and  the 
English  "Referees'  Test."3  The  original  apparatus  of  Dreh- 

1  Among  the  many  articles  upon  this  subject  there  may  be  cited  the  following: 
Briigelmann,  Z. /.  anal.  Chem.,  15  (1876),  175;  Knublauch,  Z.  f.  anal.  Chem.,  21 

(1882),  335;  Poleck,  Z./.  anal.  Chem.,  22  (1883),  171;  Fairley,  /.  Soc.  Chem.  Ind.,  5 
(1886),  283;  Drehschmidt,  Chem.  Zeitung,  n  (1887),  1382;  Hempel,  Gasanalytische 
Methoden,  3d  ed.,  1900,  p.  255;  Witzeck,  J.  Gasbelewhtung,  46  (1903),  21;  Harding, 
/.  Am.  Chem.  Soc.,  28  (1906),  537. 

2  Loc.  cit. 

3  Abady,  Gas  Analysts'  Manual,  p.  178. 


320 


GAS  ANALYSIS 


schmidt  is  fragile  and  costly,  and  because  of  these  characteristics 
it  is  inferior  to  the  modification  that  has  been  designed  by  Hem- 
pel  and  that  is  shown  in  Fig.  93. 


FIG.  93 

Determination  of  Sulphur  by  Drehschmidt-Hempel 
Method. — The  illuminating  gas  under  examination  is  measured 
in  an  experimental  gas-meter  and  then  passes  through  a  short 
piece  of  rubber  tubing  b  and  the  glass  tubing  c  into  the  flask  A , 
Fig.  93.  b  is  provided  with  a  screw  pinchcock.  The  tube  c  is 
of  hard  glass,  is  about  5  mm.  in  diameter,  is  bent  somewhat 


ILLUMINATING   GAS  —  FUEL   GAS  321 

downward  after  it  enters  the  flask  and  is  drawn  out  at  the  end  to 
a  small  opening.  The  neck  of  the  receiving  flask  A  is  drawn 
down  in  the  flame  of  the  blast  lamp  to  a  small  tube  which  is 
connected  at  d  by  means  of  a  piece  of  rubber  tubing  with  the 
absorption  apparatus  DD.  The  three-way  glass  tube  e  is  in- 
serted in  the  tubulure  of  the  flask  and  is  held  in  position  in  the 
neck  by  a  piece  of  rubber  tubing  or  a  rubber  stopper  with  a  large 
opening.  The  side  arm  of  the  three-way  piece  e  is  joined  by  the 
rubber  tube  /  to  the  cylinder  B.  This  cylinder  is  filled  with 
pieces  of  pumice-stone  upon  which  there  is  allowed  to  drop  a 
solution  of  potassium  hydroxide  from  a  separatory  funnel.  The 
air  drawn  into  the  apparatus  must  pass  through  this  tower  and 
is  there  freed  from  any  hydrogen  sulphide  which  may  be  present 
in  the  air  of  the  laboratory,  g  is  connected  with  an  ordinary 
water  suction  pump. 

In  each  absorption  bottle  DD  is  placed  20  cc.  of  a  5  per  cent 
solution  of  potassium  carbonate.  To  the  contents  of  the  first 
two  bottles  there  is  added  a  few  drops  of  bromine  to  oxidize  the 
sulphur  dioxide  to  sulphuric  acid. 

The  illuminating  gas  should  be  allowed  to  pass  through  the 
gas-meter  for  some  time  previous  to  the  beginning  of  the  deter- 
mination, to  make  sure  that  the  meter  is  completely  filled  with 
the  gas  under  examination. 

When  the  apparatus  has  thus  been  prepared  for  the  deter- 
mination, the  water  suction  pump  is  started,  and  a  rapid  current 
is  drawn  through  the  purifying  cylinder  B,  the  flask  A,  and  the 
bottles  DD.  The  tube  c  is  withdrawn  from  the  flask,  and  the 
gas  is  ignited  at  its  outlet.  The  screw  pirichcock  b  is  closed  until 
the  flame  is  about  i  cm.  long,  and  c  is  then  introduced  into  A 
and  the  cork  h  is  firmly  inserted  into  position,  c  should  be 
moved  in  or  out  through  h  until  the  flame  burns  in  the  middle  of 
the  flask.  It  should  lie  slightly  below  the  lower  side  of  the 
tubulure  of  the  flask.  In  this  position  the  flame  will  burn 
quietly  for  hours,  but  if  it  is  above  the  tubulure  it  will  go  out, 
because  in  the  upper  part  of  the  flask  the  products  of  combustion 


322  GAS  ANALYSIS 

are  not  removed  with  sufficient  rapidity  by  the  entering  current 
of  air.  By  means  of  the  screw  pinchcock  b  it  is  easy  so  to  regulate 
the  flame  as  to  cause  it  to  burn  with  sharply  denned  edges,  thus 
insuring  complete  combustion  of  the  illuminating  gas.  Note  the 
temperature  of  the  gas,  the  prevailing  barometric  pressure,  and 
the  reading  of  the  manometer  on  the  meter. 

After  about  fifty  liters  of  the  gas  has  been  burned,  read  the 
meter  accurately  and  remove  the  burner  from  the  globe.  At 
this  point  the  barometer,  the  manometer  on  the  meter,  and  the 
thermometer  should  be  read  again  and  the  average  value  should 
in  each  case  be  used  in  the  calculation  of  results. 

Rinse  the  globe  with  distilled  water  into  a  beaker.  Pour  the 
contents  of  the  three  (Muencke)  wash  bottles  into  the  beaker 
and  rinse  well  with  distilled  water.  Acidify  the  solution  with 
hydrochloric  acid  and  heat  to  boiling  in  order  to  expel  the  bro- 
mine. Add  barium  chloride  to  the  hot  solution  and  determine 
the  weight  of  barium  sulphate  in  the  usual  manner. 

The  sulphur,  which  may  exist  in  the  gas  as  hydrogen  sulphide, 
as  carbon  disulphide,  or  as  organic  sulphur  compounds,  is 
burned  to  sulphur  dioxide,  862,  which  is  oxidized  by  the  bro- 
mine to  sulphur  trioxide,  SO3,  and  this  reacts  with  the  po- 
tassium carbonate  to  form  potassium  sulphate.  Hydrochloric 
acid  is  added  to  the  solution  to  decompose  the  carbonate 
present. 

The  amount  of  sulphur  in  the  gas  is  calculated  from  the 
weight  of  the  barium  sulphate  found,  the  result  being  expressed 
in  terms  of  grams  of  sulphur  per  cubic  meter  (1000  liters)  of  the 
gas  at  o°  and  760  mm. 
Grams  sulphur  per  cubic  meter  = 

1000  ,  At.  wt.  sulphur       760  (i  +  0.00^67^) 

xx     (~p  p  \  r  •<,  2 v         °    '   '. 

V  J  Mol.  wt.  BaSO4  (B  +  b)  —  m 

In  the  above 

V    =  liters  of  gas  burned, 
P    =  grams  BaSO4  found, 


ILLUMINATING  GAS  —  FUEL  GAS  323 

Pi  =  grams  BaSC>4  found  in  blank  test  of  reagents,1 
B    =  observed  barometric  pressure, 

b    =  pressure  (in  addition  to  atmospheric)  of  gas  in  meter, 
t     =  temperature  of  gas  in  meter, 
m   =  tension  aqueous  vapor  at  P. 
At.  wt.  S 

AT  i     +  P  cr>   =  ai3732S- 
Mol.  wt.  BaSO4 

To  express  results  as  "grains  sulphur  per  100  cubic  feet  of 
the  gas,"  multiply  "grams  per  cubic  meter"  by  the  factor 
43.698. 

Schumacher  and  Feder  2  state  that  only  sulphur  dioxide  and 
no  sulphur  trioxide  is  formed  in  the  combustion  of  the  gas  in 
the  Drehschmidt  apparatus.  Upon  this  observation  they  base 
a  volumetric  method  for  the  determination  of  total  sulphur. 

A  measured  volume  of  a  solution  of  potassium  iodate  of  known 
strength,  that  contains  about  18  grams  of  potassium  iodate  to 
the  liter,  is  placed  in  the  absorption  bottles  DD,  and  the  gaseous 
products  of  the  combustion  are  drawn  through  this  liquid  in  the 
usual  manner.  The  solution  is  then  transferred  to  a  flask  and 
is  boiled  for  from  ten  to  fifteen  minutes  to  expel  the  liberated 
iodine.  The  liquid  is  then  cooled,  a  little  sulphuric  acid  is 
added,  and  the  excess  of  potassium  iodate  is  titrated  with 
sodium  thiosulphate.  The  authors  state  that  the  results  agree 
quite  satisfactorily  with  those  obtained  by  the  gravimetric 
method. 

In  the  use  of  the  Hempel  modification  of  the  Drehschmidt 
apparatus  difficulty  is  at  times  experienced  in  so  regulating  the 
combustion  in  the  flask  A  that  the  flame  will  be  non-luminous 
and  at  the  same  time  will  burn  continuously  throughout  the 
run.  Harding  states  3  that  this  difficulty  may  be  avoided  by  the 

1  The  bromine  water  and  potassium  carbonate  used  should  be  tested  qualitatively 
for  the  presence  of  sulphates.    If  the  test  gives  positive  results  the  sulphur  is  deter- 
mined in  a  quantity  of  these  reagents  equal  to  that  used  in  the  experiment. 

2  Z.  /.  Unters.  Nahr.-Genussm.,  10  (1005),  649. 

3  /.  Am.  Chem.  Soc.,  28  (1906),  537. 


324  GAS  ANALYSIS 

use  of  a  special  burner  of  hard  glass  which  is  figured  and  de- 
scribed in  his  article. 

Determination  of  Sulphur  by  Referees'  Method. —  The  of- 
ficial method  in  use  in  London,  England,  for  the  determination 
of  the  total  sulphur  in  illuminating  gas  is  known  as  the  Referees' 
Test.1 

In  this  method  the  gas  is  burned  in  air  that  contains  ammonia, 
and  the  resulting  water,  ammonium  carbonate,  ammonium 
sulphite,  and  ammonium  sulphate  are  collected  in  a  condensing 
tower.  The  products  of  combustion  are  then  dissolved  in  water, 
the  solution  is  acidified  with  hydrochloric  acid  and  is  boiled 
to  expel  carbon  dioxide.  The  sulphate  that  is  present  is  then 
precipitated  with  a  solution  of  barium  chloride.  The  accuracy 
of  the  method  has  been  called  in  question  because  of  the  pos- 
sibility of  incomplete  retention  of  the  oxides  of  sulphur  by 
the  condensing  tower,  and  further  because  of  the  probability 
that  some  of  the  sulphur  would  be  oxidized  only  to  sulphur 
dioxide,2  in  which  case  the  resulting  ammonium  sulphite  would 
be  decomposed  when  the  solution  is  boiled  with  hydrochloric 
acid  and  some  sulphur  would  escape  precipitation  as  barium 
sulphate.  These  points  have  been  investigated  in  the  Cornell 
Laboratory  by  Mr.  George  Hopp.  He  found  that  the  condensing 
tower  that  is  customarily  used  will  retain  the  oxides  of  sulphur 
if  the  rate  of  flow  of  the  gas  does  not  exceed  twenty  liters  per 
hour.  As  to  the  second  point,  however,  his  analyses  show  that 
the  Referees'  method  yields  too  low  results  unless  the  solution 
of  the  products  of  combustion  is  treated,  before  acidification, 
with  an  oxidizing  agent  that  will  convert  the  sulphite  to  sulphate. 
With  these  modifications  the  method  appears  to  give  quite 
satisfactory  results. 

In  the  Referees'  method  the  gas  is  burned  in  a  Bunsen  burner 
B,  Fig.  94,  that  stands  in  a  perforated  metal  base  D.  The  burner 

1  A  detailed  description  of  this  procedure  is  given  in  Abady's  Gas  Analysts'  Manual, 
Chapter  V. 

2  In  this  connection  see  Schumacher  and  Feder,  Zeit.  f.  Unters.  Nahr.-Genussm., 
10  (1905),  649. 


ILLUMINATING   GAS  —  FUEL  GAS 


325 


FIG.  94 

that  is  furnished  with  the  apparatus  is  a  small  Bunsen  burner 
with  a  steatite  tip.  With  an  ordinary  Bunsen  burner,  however, 
the  gas  can  be  burned  more  rapidly,  without  the  formation  of  a 


326  GAS  ANALYSIS 

smoky  flame,  than  is  possible  with  the  special  burner.  The 
products  of  combustion  pass  upward  through  the  conical  glass 
chimney  C.  The  upper  end  of  the  chimney  passes  through  a 
rubber  stopper  that  is  inserted  into  the  tubulure  of  the  cylinder 
A.  The  upper  portion  of  the  cylinder  is  filled  with  pieces  of 
glass  rod  about  40  mm.  long  and  8  mm.  in  diameter,  or  with 
glass  balls  about  15  mm.  in  diameter.  In  the  bottom  of  the 
cylinder  is  a  round  hole  into  which  is  inserted  a  rubber  stopper 
that  carries  a  glass  tube.  The  condensed  water  flows  through 
this  tube  into  the  beaker  E. 

Pieces  of  non-effloresced  ammonium  sesquicarbonate, 

((NH4)2  CO3-  2  NH4HCO3), 

about  40  grams  in  all,  are  placed  around  the  burner  on  a  per- 
forated plate  in  the  base  D.  A  few  pieces  of  the  salt  are  also 
placed  on  top  of  the  glass  rods  or  balls  in  the  cylinder.  The 
ammonia  that  is  set  free  by  the  spontaneous  decomposition 
of  this  substance  unites  with  the  sulphur  dioxide  and  prevents 
its  escape. 

The  gas  is  first  passed  through  a  gas  meter  until  all  air  has 
been  driven  from  the  meter  and  the  water  in  the  meter  is  sat- 
urated with  the  gas  under  examination.  The  meter  is  then 
connected  with  the  burner  B  and  the  gas  is  lighted  at  the  burner. 
The  flame  is  turned  down  until  the  rate  of  consumption  of  gas 
is  not  more  than  20  liters  per  hour.  A  screw  clamp  placed  upon 
the  rubber  tube  of  the  burner  furnishes  a  means  of  accurately 
adjusting  the  height  of  the  flame.  The  burner  and  the  base  D 
are  then  placed  under  the  conical  glass  chimney  and  the  upper 
end  of  the  chimney  is  at  once  inserted  into  the  opening  of  the 
cylinder  A.  Readings  of  the  meter,  the  barometric  pressure, 
the  manometer  on  the  meter  and  the  temperature  of  the  gas 
as  it  passes  through  the  meter  are  immediately  made. 

When  from  50  to  60  liters  of  gas  has  been  burned,  the  gas  is 
turned  off  and  the  instruments  that  were  read  at  the  beginning 
of  the  run  are  now  read  again.  The  averages  of  the  readings 


ILLUMINATING  GAS  —  FUEL  GAS  327 

of  the  barometer,  thermometer  and  manometer  are  used  in  the 
calculation  of  results.  The  beaker  E  is  replaced  by  a  clean  empty 
beaker  and  the  cylinder  A  is  rinsed  by  pouring  through  the  tube 
attached  to  the  upper  opening  of  the  cylinder  two  or  three  por- 
tions of  distilled  water  of  25  cc.  each.  The  chimney  C  is  also 
rinsed  out  with  distilled  water  into  the  beaker.  These  rinsings 
are  then  added  to  the  contents  of  the  first  beaker.  A  measured 
amount,  about  2  cc.,  of  saturated  bromine  water  is  added 
and  the  liquid  is  thoroughly  stirred  for  a  few  moments.1  The 
solution  is  acidified  with  hydrochloric  acid  and  is  heated  to 
boiling  to  decompose  the  carbonates  that  are  present  and  to 
expel  the  excess  of  bromine.  A  solution  of  barium  chloride  is 
then  added  and  the  precipitate  of  barium  sulphate  is  collected 
on  a  filter  and  is  washed,  dried,  and  weighed  in  the  usual  manner. 
The  amount  of  sulphur  in  the  gas  is  calculated  from  the  weight 
of  the  barium  sulphate  by  means  of  the  formula  given  on  p.  322. 
Young's  Volumetric  Method  for  Determination  of  Sul- 
phur. —  Young  has  proposed2  an  indirect  volumetric  method  for 
determining  the  sulphur  in  illuminating  gas.  The  solution  of 
the  sulphates  obtained  by  the  Referees'  method  is  treated  with 
bromine  water  in  the  manner  above  described  and  then  acetic 
acid  is  added  in  an  amount  sufficient  to  decompose  the  ammo- 
nium carbonate  3  that  is  present.  The  solution  is  then  made  up 
to  definite  volume  and  to  a  measured  portion  of  it  there  is  added 
a  measured  excess  of  a  standard  solution  of  barium  chloride. 
The  precipitated  barium  sulphate  is  not  removed  by  filtration, 
but  solution  and  suspended  precipitate  are  transferred  to  a 
platinum  or  porcelain  dish  and  the  whole  is  evaporated  to  dryness 
and  is  then  heated  to  low  redness  to  expel  the  hydrochloric  acid 
and  ammonium  chloride.  The  dish  is  allowed  to  cool  and  the  con- 

1  If  the  bromine  water  contains  sulphates,  the  amount  of  sulphur  in  the  volume  of 
this  reagent  that  is  added  should  be  subtracted  from  the  final  result.    Ammonium 
sesquicarbonate  usually  contains  no  sulphate,  but  it  nevertheless  should  be  tested 
for  this  impurity  before  being  used. 

2  Stone's  Practical  Testing  of  Gas  and  Gas  Meters,  p.  116. 

3  These  chemicals  must  be  free  from  non-volatile  halogen  salts. 


328  GAS  ANALYSIS 

tents  is  washed  out  with  distilled  water  into  a  beaker.  An  amount 
of  a  10%  solution  of  potassium  chroma te  sufficient  to  precipitate 
all  of  the  barium  chloride  and  to  color  the  supernatant  liquid 
pale  yellow  is  then  added,  and  a  standard  solution  of  silver 
nitrate  is  run  in  from  a  burette  until  the  red  color  of  silver 
chromate  remains  permanent.  The  solutions  that  are  here  used 

are  a  —  solution  of  silver  nitrate  that  contains  8.449  grams 
AgNOa  to  the  liter  and  a  — -  solution  of  barium  chloride  that 

contains  26.0375  grams  BaC^  to  the  liter.  In  the  calculation 
of  results  the  volume  of  the  gas  that  has  been  burned  is  corrected 
to  standard  conditions  (760  mm.,  O°  C.).  The  volume  of  barium 
chloride  equivalent  to  the  volume  of  silver  nitrate  that  has 
been  added  (5  cc.  AgNO3  =  i  cc.  BaCk)  is  then  calculated, 
and  this  result  is  subtracted  from  the  volume  of  barium  chloride 
that  was  added.  The  remainder  represents  the  amount  of 
barium  chloride  that  reacted  with  the  sulphate  in  the  solution. 
Knowing  the  strength  of  the  solution  of  barium  chloride,  the 
actual  weight  of  the  barium  chloride  may  then  easily  be  calcu- 
lated, and  from  this  the  grams  of  sulphur  in  the  corrected  volume 
of  gas  that  has  been  burned.  This  final  result  should  then  be 
converted  into  the  amount  of  sulphur  in  grams  per  cubic  meter 
of  the  gas,  or  in  grains  per  one  hundred  cubic  feet  of  gas. 

6.  The  Determination  of  Cyanogen  in  Coal  Gas 

For  the  determination  of  the  total  cyanogen  in  illuminating 
gas  the  method  of  Nauss  (p.  263)  may  be  used. 

PINTSCH  GAS 

Pintsch  gas  is  made  by  the  destructive  distillation  of  crude 
petroleum  or  its  distillates.  It  possesses  an  illuminating  power 
three  or  four  times  greater  than  that  of  average  coal  gas,  and  it 
can  be  brought  under  a  pressure  of  ten  atmospheres  with  a  loss 
of  only  ten  per  cent  of  its  illuminating  power.  Twenty-five 


ILLUMINATING   GAS  —  FUEL  GAS  329 

samples  of  the  compressed  gas  showed  on  analysis  the  following 
average  composition: 

Heavy  Hydrocarbons  (Illuminants) 

Benzene,  C6H6  ) 

Ethylene,  C2H4,  etc.     V        . .     .      .     35      per  cent 

Propylene,  CsHe  j 

Carbon  Monoxide,  CO       .      .      .      .      .       0.5 

Hydrogen,  H2     ......      .      .       4-5 

Methane,  CH4  I 

Ethane,  C2H6  J    ' 

In  the  analysis  of  a  sample  of  Pintsch  gas  the  constituents 
would  be  determined  in  the  order  already  given  under  illumi- 
nating gas,  namely :  — 

Carbon  dioxide  by  absorption  with  potassium  hydroxide, 

Benzene  by  absorption  with  ammonia  nickel  cyanide  and 
5  per  cent  sulphuric  acid, 

Heavy  hydrocarbons  other  than  benzene  by  absorption  with 
fuming  sulphuric  acid  and  potassium  hydroxide, 

Oxygen  by  absorption  with  alkaline  pyrogallol, 

Carbon  monoxide  by  absorption  with  ammoniacal  cuprous 
chloride, 

Hydrogen  by  fractional  combustion  with  copper  oxide 
(p.  201)  or  by  absorption  with  palladium-black  (p.  188), 

Methane  and  ethane  by  combustion  with  oxygen  in  the  com- 
bustion pipette  (p.  149),  and  calculation  of  the  percentages  of 
the  two  gases  by  the  method  set  forth  on  p.  315. 

The  high  percentage  of  heavy  hydrocarbons  in  Pintsch  gas 
renders  it  necessary  that  the  treatment  of  the  mixture  with  the 

[absorbents  for  these  constituents  be  thorough  and  sufficiently 
prolonged  to  insure  the  complete  removal  of  these  gases. 
The  large  amount  of  methane  and  its  homologues  precludes 
the  use  of  the  total  residue  in  the  final  combustion  if,  as  is 
desirable,  the  volume  of  oxygen  and  the  volume  of  the  resulting 
carbon  dioxide  are  to  be  kept  within  the  capacity  of  the  gas 


330  GAS  ANALYSIS 

burette  (100  cc.).      This  is  apparent  from  the  equations  repre- 
senting the  combustion  of  methane  and  ethane. 

CH4        +  2  O2     =  C02     +  2  H2O 

1  VOl.  2  VOl.  I  VOl. 

2  C2H6    +  7  O2     =  4  CO2  +  6  H2O 
2  vol.  7  vol.       4  vol. 

Consequently,  in  the  combustion  of  methane  and  ethane  in 
Pintsch  gas,  100  cc.  of  oxygen  is  first  passed  into  the  combustion 
pipette  and  then  only  such  portion  of  the  combustible  residue  is 
introduced  as  will  ensure  the  presence  of  an  excess  of  oxygen  in 
the  pipette  after  the  combustion  is  complete. 

It  is  not  possible,  by  means  of  one  complete  combustion,  to 
determine  more  than  two  hydrocarbons  of  the  methane  series 
(see  p.  130,  First  Case).  For  this  reason,  if  the  combustible 
residue  contains,  in  addition  to  methane  and  ethane,  a  higher 
homologue  of  the  series,  this  third  hydrocarbon  cannot  be  de- 
termined by  the  above  procedure.  It  is  usually  satisfactory, 
however,  to  consider  that  the  combustible  residue,  after  the 
removal  of  hydrogen,  contains  only  methane  and  ethane  and  to 
calculate  the  results  on  the  basis  of  that  assumption. 

PRODUCER   GAS  —  BLAST-FURNACE   GAS 

In  the  analysis  of  these  gas  mixtures  the  determination  of 
benzene  may  be  omitted  but  no  further  special  modification 
of  the  usual  procedure  is  needed  unless  the  combustible  residue 
is  to  be  determined  by  explosion.  Producer  gas  and  blast- 
furnace gas  frequently  contain  so  small  an  amount  of  com- 
bustible gas  that  the  residue  will  not  explode  when  mixed  with 
oxygen  or  air.  In  such  case  pure  hydrogen  or  oxyhydrogen 
gas  must  be  added  to  the  residue  (see  p.  144). 


CHAPTER  XVI 

THE  DETERMINATION   OF  THE  HEATING  VALUE   OF 

FUEL 

The  heating  value  of  a  fuel  is  determined  by  burning  a  known 
amount  of  the  fuel  in  an  apparatus  termed  a  fuel  calorimeter  and 
measuring  the  heat  that  is  produced.1 

Fuel  calorimeters  are  of  two  types,  continuous  and  discontin- 
uous. The  heating  value  of  solid  fuels  is  usually  determined 
with  a  calorimeter  of  the  discontinuous  form,  while  with  liquid 
and  gaseous  fuel  a  continuous  calorimeter  is  customarily  em- 
ployed. 

i.  The  Determination  of  the  Heating  Value  of  Solid  Fuels 

The  most  satisfactory  and  accurate  method  for  the  determina- 
tion of  the  heating  value  of  solid  fuel  consists  in  burning  a 
weighed  amount  of  the  fuel  with  the  aid  of  compressed  oxygen  in 
a  bomb  that  is  immersed  in  water.  -The  heat  evolved  in  the 
combustion  warms  the  water  that  surrounds  the  bomb  and  from 
this  rise  in  the  temperature  of  the  water  the  heating  value  of  the 
fuel  is  calculated. 

The  Bomb.  —  Of  the  many  forms  of  bombs  that  have  been 
devised,  the  best  known  types  are  those  of  Berthelot,  Mahler, 
Hempel,  Atwater,  Krocker,  Emerson  and  Langbein.  That 
designed  by  Mahler  will  here  be  described. 

The  Mahler  bomb  (Fig.  95)  is  a  steel  cylinder  B  of  10  cm. 
external  diameter  at  the  lower  end  and  14  cm.  high,  with  walls 

1  For  full  discussion  of  this  subject,  see  Kalorimetrische  Methodik,  by  W.  Glikin, 
IQII;  Die  kalorimetrische  Heizwertbestimmung  von  Kohle  mil  besonderer  Berucksicht- 
igung  der  Kalorimetereichung,  Jacob,  Zeitschrift  fur  chemische  Apparatenkunde,  2 
(1907),  281,  313,  337,  369,  499,  533,  565,  597;  Circular  of  the  Bureau  of  Standards, 
No.  II,  The  Standardization  of  Bomb  Calorimeters. 

331 


332 


GAS  ANALYSIS 


8  mm.  thick.  The  outer  surface  is  nickel-plated;  the  inner 
surface  is  usually  covered  with  white  enamel,  although  some  of 
the  finer  instruments  are  lined  with  platinum  or  gold.  The 

bomb  rests  in  a  nickel- 
plated  sheet  iron  saddle  H 
which  renders  possible  the 
free  circulation  of  water  be- 
tween the  bottom  of  the 
calorimeter  vessel  and  the 
bottom  of  the  bomb.  The 
bomb  is  closed  by  a  steel 
cover  C  which  also  is  nickel- 
plated  on  the  outside  and 
enamelled  on  the  inside. 
The  joint  between  the  bomb 
and  the  cover  C  is  made  gas 
tight  by  setting  into  the 
top  of  the  bomb  a  lead 
gasket  against  which  a  pro- 
jecting ring  R  on  the  under 
side  of  the  cover  impinges 
when  the  cover  is  screwed 
down  into  place.  Com- 
pressed oxygen  is  passed 
into  the  bomb  through  the 
opening  in  the  stem  of  the 
needle  valve  V  and  the  tube 
W.  The  bomb  is  closed  by 
screwing  down  the  valve  V 
until  the  conical  lower  end 
is  pressed  against  the  open- 
ing that  leads  into  the  bomb. 
A  platinum  rod  P  passes 
through  the  cover  of  the 
FIG.  95  bomb  and  is  insulated  from 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   333 

the  metal  of  the  cover.  Another  platinum  rod  S,  about  one 
mm.  in  diameter  and  of  the  form  shown  in  the  figure,  is 
fastened  to  the  lower  end  of  P  by  means  of  a  small  bind- 
ing post.  A  platinum  rod  that  carries  a  platinum  plate  F  is 
fastened  by  a  binding  post  K  to  the  lower  end  of  S.  The 
plate  F  is  about  28  mm.  in  diameter,  and  has  sides  about 
4  mm.  high.  Soldered  to  the  lower  end  of  the  tube  through 
which  the  oxygen  is  admitted  is  another  platinum  rod  which 
is  joined  by  a  binding  post  to  the  platinum  rod  T.  T  ex- 
tends downward  to  the  same  distance  as  the  branch  rod 
from  S. 

The  fuel  is  placed  in  the  platinum  pan  F  and  is  ignited  by 
passing  an  electric  current  through  a  fine  iron  wire  of  about 
0.15  mm.  diameter  that  is  wrapped  around  the  lower  ends  of  the 
wires  6*  and  T  and  rests  against  the  fuel. 

Preparation  of  Sample  of  Coal.  —  The  substance,  usually 
coal,  whose  heating  value  is  to  be  determined,  should  be  accu- 
rately sampled  and  pulverized  to  pass  a  loo-mesh  sieve.  Coal 
should  be  air-dried,  the  loss  in  weight  on  drying  being  deter- 
mined and  the  heating  value  calculated  back  to  the  undried 
coal. 

The  sample  of  the  air-dried  coal  that  is  to  be  used  for  the 
combustion  may  be  handled  with  greater  convenience  and  with 
less  danger  of  loss  if  the  coal  is  first  compressed  into  a  compact 
mass  or  briquet  by  means  of  such  a  press  as  that  shown  in  Fig.  g6. 
The  cylindrical  opening  A  in  the  steel  block  H  is  filled  with  the 
powdered  sample  which  is  then  compressed  to  a  coherent  mass 
by  turning  the  bar  B  and  driving  down  the  plunger  C.  The 
small  cylinder  of  coal  is  then  pushed  out  of  A  by  turning  the 
screw  5  upward,  inserting  the  steel  plate  P  that  carries  H  into 
the  slot  KK  and  again  driving  down  the  plunger  C  upon  the 
coal  cylinder  in  A . 

This  compression  of  the  coal  to  the  form  of  a  briquet  does  not 
appear  to  be  necessary,  so  far  as  accuracy  of  result  is  concerned, 
in  the  case  of  anthracite  coals.  These  coals  may  be  weighed 


334 


GAS  ANALYSIS 


B 


FIG.  96 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   335 

in  powdered  form  directly  into  the  platinum  pan  F.  With  bitu- 
minous coal,  however,  it  frequently  happens  that  an  appreciable 
amount  of  the  powdered  sample  is  thrown  out  of  the  platinum 
pan  by  the  violent  escape  of  volatile  matter  during  the  combus- 
tion in  the  bomb,  and,  after  the  combustion,  the  interior  of  the 
bomb  will  frequently  be  found  to  be  covered  with  a  fine,  black 
dust.  The  degree  to  which  a  powdered  bituminous  coal  may 
escape  combustion  in  the  bomb  is  shown  by  the  results  of  an 
examination  into  this  subject  made  for  the  author  by  Mr.  N.  R. 
Beagle.  Mr.  Beagle  found  that  it  was  practically  immaterial 
whether  an  anthracite  coal  be  compressed  into  a  briquet  or 
burned  in  the  powdered  form.  But  with  a  bituminous  coal  he 
obtained  an  average  result  of  7170  calories  per  gram  when  the 
fuel  was  burned  in  the  powdered  form  and  7308  calories  per 
gram  when  the  bituminous  coal  was  briqueted.  The  interior  of 
the  bomb  after  combustion  showed  unburned  coal  dust  in  each 
case  when  powdered  coal  was  used,  whereas  when  the  coal 
briquet  was  employed,  none  of  this  powder  was  visible  after 
combustion. 

If  the  coal  is  compressed,  the  little  cylinder  of  coal  is  freed 
from  coal  dust  by  brushing  it  with  a  camals'  hair  brush  and  is 
then  trimmed  with  a  knife  to  the  proper  weight.  The  coal 
sample  should  weigh  about  one  gram.  The  sample,  E,  is  then 
placed  in  the  platinum  pan  F  and  is  accurately  weighed. 

The  Calorimeter.  —  The  calorimeter  vessel  is  a  nickel-plated 
metal  cylinder  /  (Fig.  97)  that  should  be  just  large  enough  to 
permit  of  complete  immersion  of  the  bomb  and  thorough  stirring 
of  the  water.  It  is  supported  in  a  double- walled  metallic  vessel  K 
that  is  enamelled  on  the  surface  next  to  the  calorimeter,  and  is 
provided  with  a  metallic  cover  that  has  openings,  w  w,  through 
which  this  jacket  may  be  filled  with  water.  This  vessel  is  further 
covered  on  the  sides  and  top  and  bottom  with  a  layer  of  felt 
about  one  centimeter  thick.  The  calorimeter  vessel  is  placed 
within  the  jacket  vessel  K  in  the  position  shown  in  the  figure  and 
this  inner  opening  of  K  is  provided  with  a  cover  R  that  is  made 


336 


FIG.  97 

in  two  pieces  and  that  has  openings  through  which  pass  the 
thermometer  T  and  the  rods  of  the  stirrer  55.  The  thermometers 
that  are  used  in  this  work  are  usually  filled  with  mercury  and 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   337 

have  the  scale  marked  on  the  stem.  They  should  cover  a  range 
of  10°  to  15°  C.  with  graduations  in  0.01°,  or  should  be  of  the 
Beckmann  type  with  a  scale  range  of  about  six  degrees.  Before 
being  placed  in  use  the  thermometers  should  be  tested  and  the 
corrections  for  errors  in  the  scale  ascertained.  The  stirrer  may 
be  run  by  a  motor  or  may  be  operated  by  hand.  The  stirring 
should  be  slow  and  in  all  cases  as  uniform  as  possible. 

The  calorimeter  vessel  should  not  rest  directly  upon  the  metal 
jacket  but  should  stand  upon  supports  PP  of  glass,  porcelain 
or  ebonite.  The  stirrer  should  be  of  the  screw  type,  but  should 
move  straight  up  and  down.  The  rotary  movement  of  the  stir- 
rer in  the  usual  form  of  Mahler  calorimeter  makes  it  impossible 
to  adequately  cover  the  inner  calorimeter  vessel. 

Preparation  of  the  Bomb.  —  Clean  the  inside  of  the  bomb 
and  polish  the  nickel  surface  of  the  bomb  and  its  cover.  Place 
the  cover  of  the  bomb  in  an  upright  position  in  a  clamp  or  on 
a  ring  stand.  Wind  a  piece  of  iron  ignition  wire  (see  above) 
about  3  cm.  long  around  a  pin  to  give  it  spiral  form  and  then 
weigh  the  wire.  If  the  apparatus  is  in  frequent  use,  it  will  be 
found  more  convenient  to  ascertain  the  weight  of  the  ignition 
wire  per  linear  centimeter  and  then  to  measure  the  length  of 
the  piece  that  is  used. 

Wrap  the  ends  of  the  ignition  wire  around  the  platinum  wires 
61  and  T  (see  Fig.  95).  Clean  the  platinum  plate  F,  place  within 
it  the  weighed  coal  briquet  E  or  the  powdered  coal,  and  then 
fasten  it  to  5  by  means  of  the  small  binding  post  K  in  such  posi- 
tion that  the  spiral  of  ignition  wire  rests  lightly  against  the  top 
of  the  coal.  4 

Introduce  from  0.5  to  one  cc.  of  water  into  the  bomb,  place 
upon  the  bomb  the  cover  carrying  the  coal  sample,  screw  down 
the  cover  with  the  hand,  and  finally  set  it  down  firmly  with  a 
wrench. 

To  fill  the  bomb  with  compressed  oxygen,  proceed  as  follows: 

Connect  to  U,  Fig.  95,  by  means  of  a  nut  the  flexible  copper 
tube  L  (Fig.  98)  that  leads  to  the  manometer  M  and  the  oxygen 


338 


FIG.  98 
tank  O.1   Open  the  valve  of  the  oxygen  tank  slowly  and  allow  the 

1  The  oxygen  should  of  course  contain  no  combustible  gases  such  as  carbon  mo- 
noxide, hydrogen  or  hydrocarbons. 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   339 

pressure  in  the  bomb  to  rise  to  about  five  atmospheres.  Close  the 
valve  of  the  bomb,  disconnect  the  copper  tube  L,  and  then  care- 
fully open  the  valve  F,  Fig.  95.  This  operation  serves  to  rinse 
out  the  bomb  with  oxygen  and  thus  to  remove  the  greater  part 
of  the  nitrogen  of  the  air  that  was  originally  in  the  bomb.  This 
is  done  to  prevent  the  formation  of  an  appreciable  amount  of 
nitric  acid  from  atmospheric  nitrogen  during  the  combustion.  The 
correction  for  the  heat  of  formation  of  nitric  acid  is,  however, 
usually  less  than  six  calories,  a  value  so  small  that  the  rinsing 
of  the  bomb  with  oxygen  may  be  omitted  in  most  commercial 
work. 

Now  connect  L  again  with  U,  open  the  valve  of  the  oxygen 
tank  carefully  and  fill  the  bomb  with  oxygen  to  a  pressure  of 
25  atmospheres.  Close  the  valve  V  and  disconnect  L. 

Combustion  of  the  Sample.  —  Fill  the  jacket  space  of  the 
calorimeter  with  water  of  a  temperature  about  that  of  the  room. 
Place  the  bomb,  prepared  for  the  combustion  as  above  described, 
in  the  calorimeter  and  connect  its  terminals  by  wires  with  the 
apparatus  that  is  to  furnish  the  electric  current  for  the  heating 
of  the  iron  ignition  wire.  Storage  cells  or  dry  cells  that  will 
yield  a  current  of  a  potential  of  not  more  than  15  volts  should 
be  employed.  If  a  no- volt  lighting  circuit  is  used  there  is 
danger  of  arcing  and  consequent  evolution  of  heat  within  the 
bomb.  The  battery  and  ignition  wire  should  previously  be 
tested  to  make  sure  that  the  current  will  heat  the  wire  to  in- 
candescence in  the  space  of  one  second.  Pour  into  the  calo- 
rimeter vessel  that  contains  the  bomb  a  weighed  amount  of 
water  of  a  temperature  of  from  ij4°  to  2°  below  that  of  the 
room.  The  same  amount  of  water  should  be  used  in  all  com- 
bustions. The  volume  necessary  for  the  complete  immersion 
of  the  bomb  will  vary  in  different  calorimeters  from  about 
2200  cc.  to  2700  cc. 

Introduce  the  stirrer  and  the  thermometer  and  then  put  on 
the  cover  of  the  calorimeter.  Begin  stirring  and  continue  it 
for  about  five  minutes.  At  the  end  of  this  time  the  temper- 


340  GAS  ANALYSIS 

ature  should  be  constant  or  should  be  regularly  and  only 
slightly  rising  or  falling.  Now  begin  readings  of  the  thermom- 
eter in  the  calorimeter,  noting  the  time  in  hours,  minutes  and 
seconds,  and  repeat  these  readings  every  minute  for  a  period 
of  five  minutes  in  all.  These  five  readings  cover  what  is  termed 
the  "preliminary  period."  Throughout  the  whole  experiment 
the  water  in  the  calorimeter  should  be  stirred  at  a  uniform  rate 
between  all  readings. 

At  the  end  of  the  preliminary  period,  throw  in  the  switch 
(preferably  exactly  on  an  even  minute)  and  ignite  the  sub- 
stance. Throw  out  the  switch  at  the  end  of  one  second.  Read 
the  thermometer  every  twenty  seconds,  recording  the  time  of 
each  reading  as  before.  Continue  these  readings  every  twenty 
seconds  until  the  maximum  temperature  has  been  reached 
and  the  temperature  begins  to  fall.  This  ends  the  "middle 
period." 

From  this  point  make  readings  one  minute  apart  over  a  period 
of  time  equal  to  the  length  of  the  preliminary  period.  This 
constitutes  the  "after  period."  Remove  the  bomb  from  the 
calorimeter  and  slowly  open  the  valve  to  relieve  the  excess  of 
gas  pressure  within  the  bomb.  Then  unscrew  the  cover  of  the 
bomb  and  examine  the  interior  of  the  bomb  to  make  sure  that 
the  fuel  was  completely  burned. 

The  Water  Equivalent  of  the  Calorimeter.  —  When  a  sam- 
ple of  fuel  is  burned  in  the  bomb,  the  greater  part  of  the  heat 
that  is  evolved  is  transferred  to  the  surrounding  water  which  is 
thereby  raised  in  temperature.  The  remainder  of  the  heat  is 
taken  up  by  the  apparatus  itself.  Each  particular  apparatus  will 
have  a  definite  heat  capacity  of  its  own,  which  will  be  different 
from  that  of  another  apparatus  even  of  the  same  type.  It  is  cus- 
tomary to  express  the  heat  capacity  of  the  instrument  in  terms 
of  the  number  of  grams  of  water  that  would  be  raised  i°C.  in 
temperature  by  the  heat  absorbed  by  the  apparatus.  This 
result  is  termed  the  Water  Equivalent  of  the  calorimeter.  It 
should  experimentally  be  ascertained  with  great  care  for  each 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   341 

instrument,  because  an  error  in  this  will  affect  all  determina- 
tions made  with  the  calorimeter. 

The  water  equivalent  of  most  of  the  bomb  calorimeters  now 
on  the  market  is  determined  by  the  manufacturer  and  is  marked 
upon  the  instrument.  If,  however,  the  calorimeter  is  not  so 
marked,  or  if  the  operator  deems  it  desirable  to  ascertain  the 
correctness  of  the  marking,  the  water  equivalent  of  the  ap- 
paratus may  be  determined  once  and  for  all  — 

(a)  By  weighing  the  different  parts  of  the  apparatus,  multi- 
plying the  weight  of  each  part  by  the  specific  heat  of  the 
material  of  which  that  part  is  made,  and  adding  the  re- 
sults: or 

(b)  By  the  method  of  mixtures: 1  or 

(c)  By  setting  free  a  known  amount  of  heat  within  the  bomb 
and  ascertaining  the  resulting  rise  of  temperature  of  the  water 
in  the  calorimeter  vessel.     The  most  accurate  results  by  this 
method  are  obtained  by  the  insertion  of  an  electric  resistance 
heater  within  the  bomb,  but  usually  the  determination  is  made 
by  burning  in  the  bomb  a  weighed  sample  of  a  combustible 
substance  whose  heat  of  combustion  has  accurately  been  as- 
certained. 

Standard  Combustible  Substances.  —  The  combustible 
substances  in  most  general  use  as  standards  are  cane  sugar, 
benzoic  acid  and  naphthalene.  Samples  of  these  substances, 
specially  prepared  for  this  purpose,  may  be  obtained  from  the 
Bureau  of  Standards  at  Washington.  Circular  No.  n  of  the 
Bureau  contains  the  following  statement  concerning  these  three 
materials : 

"  Sucrose  is  not  volatile  nor  strongly  hygroscopic,  but  is  rather 
difficult  to  ignite  and  sometimes  does  not  burn  completely. 
It  has  a  heat  of  combustion  of  about  3950  calories,  or  only 
about  half  that  of  the  average  coal.  The  more  exact  value  for 
each  sample  will  be  given  in  the  certificate. 

"Benzoic  acid  is  only  slightly  volatile,  is  not  very  hygroscopic, 
1  See  Jakob,  Z.  f.  chem.  Apparatenkunde,  n  (1907),  533. 


342 


GAS  ANALYSIS 


has  a  heat  of  combustion  of  about  6320  calories  and  burns  more 
readily  than  sugar. 

"Naphthalene  is  quite  volatile  but  not  hygroscopic;  it  has  a 
heat  of  combustion  of  about  9610  calories,  a  little  higher  than 
that  of  most  coals,  and  it  ignites  and  burns  very  readily. 

"Of  these  materials  probably  the  most  satisfactory  for  work 
of  the  highest  accuracy  is  benzoic  acid,  but  for  calibration  of 
commercial  calorimeters  to  an  accuracy  of  o.i  per  cent  naph- 
thalene has  some  advantages.  The  loss  by  sublimation  from 
samples  of  naphthalene  made  up  into  briquets  will  hardly  ex- 
ceed o.i  or  0.2  per  cent  in  an  hour." 

This  last  mentioned  method  is  the  most  satisfactory  for  the 
calibration  of  commercial  calorimeters.  It  is  carried  out  as  fol- 
lows: Compress  some  of  the  standard  combustible  substance  in 
the  press  into  the  form  of  a  briquet,  trim  it  down  until  it  weighs 
about  one  gram,1  free  it  from  loose  particles  and  dust,  and  burn 
it  in  the  calorimeter  in  the  manner  already  described. 

EXAMPLE  OF  THE  DETERMINATION  OF  THE  WATER  EQUIVA- 
LENT OF  A  CALORIMETER 
Readings  on  Beckmann  Thermometer  During  the  Experiment 


PRELIMINARY  PERIOD 

MIDDLE 

PERIOD 

AFTER 

PERIOD 

Time             Temp. 

Time 

Temp. 

Time 

Temp. 

2:30:00       2.430° 

2:35:20 

2-54° 

2:41:30 

4-750° 

31:00       2.434 

36:00 

3-26 

42:00 

4-747 

32:00       2.438 

36:20 

4.16 

43:00 

4-743 

33:00        2.443 

36:40 

4.46 

44:00 

4-737 

34:00       2.446 

37:00 

4.62 

•     45:00 

4-732 

35:00      ^2.450 
Sample  ignited 

37:20 
37:40 

4.70 
4-73 

46:00 

-  •    - 

4-728 

38:00 

4-75 

38:20 

4-751 

38:40 

4-752 

39:00 

4-753 

39:20 

4-753 

39:40 

4-753 

40:00 

4-753 

40:20 

4-753 

40:40 

4-  753 

41  :oo 

4-753 

1  The  amount  of  the  substance  should  be  such  as  will  cause  about  the  same  rise  in 
temperature  in  the  calorimeter  as  that  which  results  from  the  combustion  of  about 
one  gram  of  the  fuels  that  are  later  to  be  tested. 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   343 

Weight  of  sample  of  benzoic  acid  .  .  i .  0020  grams 

Weight  of  water  in  calorimeter     ,  •  .  .  2250  grams 

Weight  of  iron  ignition  wire    .     •'.  .  .  0.004  gram 

Pressure  of  oxygen  in  the  bomb  .  .  .  25  atmospheres 


Reading  of  thermometer  at  end  of  middle 

period     .      .      ...      .      •  .  •     •      •  4-753° 

Reading  of  thermometer  at  beginning  of 

middle  period    ........  2.450° 

Observed  rise  of  temperature     .     .      .     •. 

Radiation  correction  (see  below) 

Corrected  rise  of  temperature    ....  2.322' 


Heat  of  combustion  of  benzoic  acid  in  cal- 
ories per  gram  .  . 632O 

Heat  evolved  by  combustion  of  sample  of 

benzoic  acid  taken  .^  ....  •  1.0020  X  6320  =  6332.6  cals. 

Heat  of  combustion  of  iron  in  calories  per 

gram l6oo 

Heat  evolved  by  combustion  of  ignition 

wire  ....  0.004  X  1600  =  6. 4  cals. 

Heat  evolved  by  combustion  of  sample      .  6339      ca|s 


Total  weight  of  water  that  would  be  raised 

i°  C.  in  temperature  by  heat  evolved     .  6339 

2  322   =  273°  grams. 

Water  equivalent  of  calorimeter,  or  total 
weight  of  water  that  would  be  raised  one 
degree  in  temperature,  less  the  weight  of 
the  water  in  the  calorimeter  vessel  .  .  2730  —  2250  =  480  grams. 


The  Radiation  Correction.  —  If  the  calorimeter  could  be  per- 
fectly insulated  from  its  surroundings,  the  only  temperature 
observations  that  would  be  necessary  for  the  determination  of 
the  water  equivalent  of  the  apparatus  or  of  the  heating  value  of  a 
fuel  would  be  the  temperature  of  the  water  before  the  ignition 
and  after  the  combustion.  Perfect  insulation  is,  however,  im- 
possible, and  there  is  a  continuous  transfer  of  heat  between  the 
calorimeter  and  its  surroundings,  due  to  conduction,  radiation, 


344  GAS   ANALYSIS 

convection  currents  of  air  and  evaporation  of  water  in  the  calo- 
rimeter. This  heat  transfer  will  affect  the  thermometric  readings 
and  consequently  a  correction,  termed  the  radiation  correction, 
must  be  applied  to  eliminate  the  errors  due  to  gain  or  loss  of 
heat  by  the  calorimeter  during  the  determination.  Among  the 
various  methods  for  ascertaining  the  radiation  correction  that 
are  in  use,1  the  following  will  be  found  satisfactory  and  suffi- 
ciently accurate  for  commercial  work.  In  this,  the  average  rate 
of  heat  transfer  between  the  calorimeter  and  its  surroundings 
during  a  period  of,  say,  five  minutes,  before  the  ignition  of  the 
fuel,  "Initial  Radiation  Rate,"  and  for  a  like  period  after  the 
maximum  temperature  resulting  from  the  combustion  has  been 
reached,  "Final  Radiation  Rate,"  is  computed.  The  time  at 
which  the  mean  temperature  of  the  combustion  period  is  reached 
is  then  calculated,  and  the  initial  radiation  correction  is  com- 
puted for  the  first  part  of  the  middle  period,  and  the  final  radia- 
tion correction  for  the  last  part.  From  these  results  the  corrected 
rise  in  temperature  during  the  combustion  is  obtained.  The 
radiation  correction  is  determined  for  each  run  of  the  calorimeter. 
In  the  example  of  the  determination  of  the  water  equivalent  of 
the  apparatus  given  above  the  radiation  correction  is  calcu- 
lated in  the  following  manner: 

Radiation  Rate,  Preliminary  Period,  = 

2.450°  -2.430°  o 


5 
Radiation  Rate,  After  Period,  = 

4.753°  -  4.7280 
5 


=  0.005°  per  minute 


1  See  Experimental  Engineering  by  Carpenter   and   Diederichs,    7th   ed.,    1911, 
p.  482. 

2  This  correction  is  positive  if  the  temperature  is  falling  during  the  preliminary 
period  and  negative  if  it  is  rising. 

3  This  correction  is  positive  if  the  temperature  is  falling  during  the  after  period 
and  negative  if  it  is  rising. 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   345 


Mean  Temperature  of  Middle  Period 


2.450°  +  4-753° 


Time  at  which  mean  temperature  was  reached  (ascertained  by 

plotting  curve,  or  by  interpolation),  2:36:10. 

Portion  of  middle  period  to  which  correction  for  "preliminary" 

radiation  rate  is  to  be  applied,  2:36:10  —  2:35   = 

i  min.,  10  sec.   =  i^  min. 

Portion  of  middle  period  to  which  correction  for  "after"  radia- 
tion rate  is  to  be  applied,  2:41:00  —  2:36:10  = 
4  min.,  50  sec.   =  4-f-  min. 

Radiation  Correction  = 
0.005°  X  4-jj-  —  0.004°  X  *  e    =  0-OI9° 

Example  of  the  Determination  of  the  Heating  Value  of  a 
Sample  of  Coal. — 

Weight  of  sample  of  coal i .  0050  grams 

Weight  of  water  in  the  calorimeter        .      .         2250  grams 
Weight  of  iron  ignition  wire        ....       o .  004  gram 
Pressure  of  oxygen  in  bomb        ....  25  atm. 


PRELIMINARY  PERIOD 

MIDDLE 

PERIOD 

AFTER 

PERIOD 

Time            Temp. 

Time 

Temp. 

Time 

Temp. 

11:02:00        2.QIO0 
03              2.916 
04              2.922 
05              2.928 
06              2.934 

11:07:20 
07:40 
08:00 
08:20 
08:40 

2.96° 
3-03 
3-18 
3-70 

4.22 

11:14:00 
15:00 
1  6:00 
17:00 
1  8:00 

5-498° 
5-493 
5-490 
5.486 
5-482 

07              2.940 
Coal  ignited 

09:00 
09:20 
09:40 

4.70 
5-06 
5-26 

10:00 
10:20 

5-40 
5.46 

10:40 

S-49 

11:00 

5-500 

11:20 

5-Soi 

11:40 

5-502 

12:00 

5-502 

12:20 

5-502 

12:40 

5-502 

13:00 

5-502       • 

346  GAS  ANALYSIS 

From  these  data  the  heating  power  of  the  coal  is  calculated  by 
use  of  the  formula: 

(W  +  E)  (T  *  R)  -  C 
±1   =  


in  which  H  represents  the  heating  value  of  the  fuel,  W  the  weight 
of  the  water  in  the  calorimeter  vessel,  E  the  water  equivalent  of 
the  calorimeter,  T  the  rise  in  temperature  caused  by  the  com- 
bustion, R  the  radiation  correction,  C  the  heat  of  combustion  of 
the  iron  ignition  wire,  and  G  the  weight  in  grams  of  the  sample 
of  fuel. 
In  the  above  example 

W  =  2250  grams 

E    =  480  grams 

T    =  2.562°  C. 

R    =  +  0.007°  C. 

C    =6.4  calories  1 

G    =  1.0050  grams 
„       (W  +  E)  (T  +  R)  —  C 
~G~ 

(2250  +  480)  (2.562  +  0.007) —  6.4 

=6972  calories  per  gram. 

1.005 

It  is  customary  in  this  country  to  express  the  heating  value  of 
a  fuel  in  terms  of  British  thermal  units  2  (B.  T.  U.)  per  pound  of 

1  Correction  is  sometimes  introduced  for  the  heat  of  formation  of  nitric  acid  that 
is  formed  by  the  oxidation  of  nitrogen  gas  in  the  bomb.    This  is  done  by  washing 
out  the  bomb  with  distilled  water  after  the  combustion  and  titrating  the  acid  with 
a  standard  solution  of  an  alkali.    The  correction  is  so  small  that  it  may  be  disre- 
garded in  commercial  work.    If  the  bomb  is  rinsed  with  oxygen  gas  before  the  com- 
bustion, the  amount  of  nitric  acid  that  is  formed  from  the  atmospheric  nitrogen  in 
the  bomb  will  be  so  slight  as  to  be  negligible  even  in  quite  accurate  work.    Moreover 
sulphurous  acid  and  sulphuric  acid  that  result  from  the  combustion  of  the  sulphur 
in  the  coal  are  frequently  found  in  the  bomb  after  the  combustion.    The  presence 
of  these  compounds  will  vitiate  the  titration  results  for  nitric  acid.    Furthermore 
their  heat  of  formation  should  not  be  subtracted  from  the  heating  value  of  the  fuel. 

2  A  British  thermal  unit  is  the  amount  of  heat  required  to  raise  the  temperature 
of  one  pound  of  water  one  degree  Fahrenheit. 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   347 

coal,  instead  of  in  calories  per  gram.  The  latter  expression 
multiplied  by  1.8  gives  the  B.  T.  U.  per  pound.  Consequently 
in  the  foregoing  example 

H  =  6972  x  1.8  =  12549.6  B.  T.  U.  per  pound. 

2.  The  Determination  of  the  Heating  Value  of  Liquid  and  Gaseous 

Fuels 

The  heating  value  of  some  liquid  fuels  may  be  determined 
by  dropping  the  liquid  on  a  small  cellulose  block  1  and  then 
burning  this  in  the  usual  manner  in  a  bomb  calorimeter.  The 
determination  is,  however,  customarily  made  with  a  calorim- 
eter of  the  continuous  type,  such  as  that  devised  by  Junkers. 
This  instrument  is  primarily  designed  for  use  with  gaseous  fuels, 
but  by  means  of  special  attachments  it  may  be  employed  with 
liquid  fuels  as  well. 

The  Junkers  Gas  Calorimeter 

The  calorimeter  (Fig.  99)  consists  of  an  upright  combustion 
chamber  28  through  which  the  products  of  combustion  from 
the  flame  27  first  rise,  then  pass  downward  through  thin-walled 
copper  tubes  (shown  in  the  cross  section)  and  finally  escape 
through  ji  and  32.  The  rate  of  escape  of  these  gases  is  controlled 
by  the  damper  jj  and  their  temperature  is  shown  by  a  thermome- 
ter inserted  through  an  opening  in  the  top  of  the  pipe  32.  The 
water  vapor  in  the  combustion  gases  is  partially  condensed  and 
this  condensed  water  flows  out  through  35.  Cold  water  enters 
the  apparatus  at  3,  passes  downward  through  6,  rises  around 
the  bulb  of  the  thermometer  ij  and  then  enters  the  calorimeter 
and  passes  upward  through  the  space  around  the  heating  tubes. 
At  the  top  of  the  calorimeter  the  warmed  water  flows  through 
the  perforated  plates  38'  which  have  staggered  holes  to  promote 
thorough  mixing.  It  passes  out  of  the  apparatus  through  18,  20 
and  21  either  to  the  measuring  apparatus  or  to  waste.  The 

1  See  Kellner,  Landwirtschaftl.  Versuchsstat.,  47  (1896),  275. 


348  GAS  ANALYSIS 

water  is  warmed  in  its  passage  through  the  calorimeter;  the 
temperature  of  the  inlet  water  is  measured  by  the  thermometer 


FIG.  99 

15  and  that  of  the  escaping  water  by  the  thermometer  43.  The 
calorimeter  is  surrounded  by  a  polished  nickel-plated  jacket 
36.  The  rate  of  the  flow  of  the  water  is  regulated  by  means  of 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   349 

the  plug  cock  9  and  a  pointer  and  scale  shown  in  the  figure  to 
the  right,  and  the  head  is  kept  constant  by  the  overflow  device  4. 
The  rate  of  flow  of  the  gas  whose  heating  power  is  being  deter- 
mined is  regulated  by  the  cock  22. 

The  rate  of  flow  of  the  water  and  the  gas  should  be  so  ad- 
justed that 

(1)  the  escaping  gases  shall  have  approximately  the  same 
temperature  as  the  surrounding  atmosphere,  and 

(2)  the  difference  in  the  temperatures  of  the  entering  water 
and  the  escaping  water  shall  be  from  5°  to  10°,  or  sufficiently 
great  to  permit  of  accuracy  in  the  heat  calculations. 

The  determination  of  the  heating  power  of  a  gas  by  the  Jun- 
kers method  is  carried  out  as  follows: 

Preparation  of  Apparatus.  —  Level  and  adjust  the  experi- 
mental gas  meter  G  (Fig.  100)  and  the  pressure  regulator  at  its 
right,  and  fill  each  with  the  proper  amount  of  water.  Connect 
them  together  with  tubing  and  connect  the  inlet  tube  of  the  gas 
meter  with  the  holder  or  main  containing  the  gas  to  be  examined. 
Attach  the  burner  to  the  outlet  tube  of  the  pressure  regulator  by 
means  of  rubber  tubing,  place  the  burner  on  the  table,  turn  on 
the  gas  and  light  it  at  the  burner.  Allow  the  gas  to  burn  for 
about  fifteen  minutes  to  insure  the  saturation  of  the  water  in  the 
meter  and  pressure  regulator  with  the  constituents  of  the  gas  mix- 
ture, and  the  removal  of  air  from  these  instruments  and  from  the 
connecting  tube.  In  the  meantime  place  the  calorimeter  in  the 
position  shown  in  the  figure,  and  level  it  by  means  of  the  screws 
at  the  lower  ends  of  the  legs.  The  apparatus  should  be  protected 
from  drafts,  and  the  temperature  of  the  room  should  be  as  nearly 
constant  as  possible.  Place  the  thermometers  73,  43  and  32, 
Fig.  99,  in  place  and  connect  3  with  the  water  supply  by  means  of 
a  rubber  tube.  The  entering  water  should  have  a  temperature 
slightly  lower  than  that  of  the  room.  Turn  on  the  water,  and 
by  means  of  the  pointer  E  adjust  its  rate  of  flow  so  that  some 
of  the  entering  water  will  overflow  and  pass  out  through  4 
and  5. 


350 


GAS  ANALYSIS 


Regulate  the  air  supply  to  the  burner  to  give  a  flame  with  a 
slightly  luminous  tip  which  will  insure  the  perfect  combustion  of 
the  entering  gas  and  will  prevent  the  cooling  of  the  flame  through 
an  excess  of  air. 


G— 


;Tb  drain 


FIG.  100 


Now  insert  the  burner  in  the  combustion  chamber  and  screw 
it  firmly  into  place  in  such  position  that  the  vertical  tube  will 
project  about  12  cm.  upward  into  the  combustion  chamber.  A 
mirror  held  at  an  angle  below  the  combustion  chamber  will 
enable  the  operator  to  see  into  the  chamber  and  observe  whether 
the  burner  is  set  in  place  in  the  middle  of  the  chamber  and 
whether  the  gas  is  burning  properly. 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   351 

Regulate  the  water  supply  by  means  of  the  pointer  so  that 
there  is  a  difference  of  from  5°  to  10°  between  the  temperatures 
of  the  entering  water  and  of  that  leaving  the  calorimeter.  Read 
the  thermometer  inserted  at  32  and  note  whether  the  escaping 
gases  have  approximately  the  temperature  of  the  room.  If 
they  have  not,  adjust  the  rates  of  flow  of  the  water  and  gas 
until  this  result  is  attained.  When  the  temperatures  of  the 
escaping  water  and  of  the  escaping  gases  have  become  constant 
and  the  condensed  water  has  begun  regularly  to  drop  from  the 
tube  35  the  actual  determination  of  the  heating  value  may  be 
begun. 

Determination  of  the  Heating  Value  of  the  Gas.  —  Read 
and  record  the  prevailing  barometric  pressure,  the  temperature  of 
the  gas  in  the  meter  and  the  pressure  of  the  gas  on  the  manome- 
ter of  the  regulator.  At  the  moment  that  the  large  hand  of  the 
gas  meter  passes  the  zero  mark,  note  the  position  of  the  small 
hand  of  the  meter  and  at  once  insert  into  the  graduated  cylinder 
of  2000  cc.  capacity  the  rubber  tube  C  that  is  connected  with  the 
outlet  21  and  that  has  up  to  this  time  been  connected  with  the 
drain.  Place  a  100  cc.  graduated  cylinder  under  the  tube  35  to 
catch  the  condensed  water.  When  the  large  graduated  cylinder 
becomes  filled  to  the  upper  mark  it  is  replaced  for  the  moment 
by  a  beaker  and  is  emptied.  It  is  then  immediately  returned 
to  its  position  under  the  rubber  tube  and  the  water  that  has 
run  into  the  beaker  is  poured  into  the  cylinder.  The  number 
of  times  that  the  cylinder  is  emptied  during  the  determination 
must,  of  course,  be  accurately  recorded. 

Read  the  thermometers  1 3  and  43  at  one-half  minute  intervals. 
When  from  30  to  50  liters  of  gas  has  been  burned,  note  accu- 
rately the  reading  of  the  gas  meter  and  at  once  remove  the  rubber 
tube  from  the  large  cylinder  and  withdraw  the  small  cylinder  in 
which  the  condensed  water  is  being  collected.  Record  the  vol- 
ume of  water  that  has  been  measured  in  the  large  cylinder  and 
the  volume  of  the  condensate  that  is  collected  in  the  small  gradu- 
ated cylinder.  Again  read  the  temperature  of  the  gas  in  the  me- 


352  GAS  ANALYSIS 

ter  and  the  pressure  that  is  shown  on  the  manometer  of  the  regu- 
lator. Then  turn  off  the  gas  and  after  this  has  been  done,  shut 
off  the  water. 

Calculation  of  Results.  —  Average  the  readings  of  the  tem- 
perature of  the  gas  in  the  meter  and  of  the  pressure  on  the  ma- 
nometer of  the  regulator  at  the  beginning  and  the  end  of  the  ex- 
periment and  use  the  mean  values  in  the  calculation  of  results. 

Reduce  the  volume  of  gas  that  has  been  burned  to  the  volume 
that  it  would  occupy  under  standard  conditions  with  the  aid  of 
the  formula 

p+  s  —  m 

VQ      =     1) 

760    (l       +     0.00367    /) 

in  which 

VQ  represents  the  volume  of  the  gas,  in  liters,  under  standard 
conditions, 

v  represents  the  volume  of  the  gas,  in  liters,  under  the  pre- 
vailing conditions, 

p  represents  the  barometric  pressure  in  millimeters  of  mercury, 

5  represents  the  reading  of  the  manometer  on  the  meter,  in 
millimeters  of  mercury, 

m  represents  the  tension  of  water  vapor  at  t°,  in  millimeters 
of  mercury, 

/  represents  the  temperature  of  the  gas  in  the  meter. 

The  heat  evolved  by  the  combustion  of  the  gas  may  be  ex- 
pressed as  total  heat,  gross  heat,  or  net  heat.1  Rosa  defines  total 
heat  as  the  amount  of  heat  measured  by  the  calorimeter  per 
unit  quantity  of  gas  burned,  if  the  air  (admitted  to  the  calorim- 
eter at  room  temperature)  is  dry,  and  if  all  of  the  water  vapor 
formed  by  combustion  is  condensed  in  the  calorimeter,  and  both 
it  and  the  products  of  combustion  escape  at  room  temperature. 
Gross  heat  is  the  amount  of  heat  measured  by  the  calorimeter 
when  the  gas  and  the  air  are  admitted  to  the  calorimeter  at 
room  temperature,  but  are  not  dry,  and  when  the  products  of 
combustion  are  cooled  substantially  to  room  temperature  be- 

1  Rosa,  The  use  of  Gas  for  Heat  and  Power,  Centenary  Celebration  Lectures,  p.  143. 


DETERMINATION  OF  HEATING  VALUE  OF  FUEL   353 

fore  leaving  the  calorimeter,  these  products  escaping  as  gases  ex- 
cept for  a  small  amount  of  water  vapor  that  is  condensed  and 
collected  as  water  at  room  temperature.  The  net  heating  value 
of  a  gas  is  the  total  heating  value  minus  the  latent  heat  at  room 
temperature  of  all  of  the  water  vapor  that  is  formed  in  the  com- 
bustion. 

The  gross  heating  value  of  the  gas  may  be  calculated  by 
means  of  the  formula 


in  which 

H  represents  the  heating  value  of  the  gas  expressed  in  calories 
per  liter, 

W  represents  the  number  of  cubic  centimeters  of  water  that 
has  been  heated, 

T  represents  the  average  difference  in  the  readings  of  the 
thermometers  ij  and  43, 

V  represents  the  volume  of  gas  in  liters,  under  standard  con- 
ditions, that  has  been  burned. 

The  net  heating  value  of  the  gas  may  be  calculated  by  means 
of  the  formula 


in  which 

Hr  represents  the  lower  heating  value  of  the  gas  expressed 
in  calories  per  liter, 

W  as  above, 

T  as  above, 

V  as  above, 

W  represents  the  number  of  cubic  centimeters  of  water  con- 
densed during  the  combustion  of  the  gas. 

/  represents  the  temperature  of  the  condensed  water  escaping 
from  35,  Fig.  99. 


354  GAS  ANALYSIS 

To  express  the  heating  power  of  a  gas  in  B.  T.  U.  per  cubic 
foot,  multiply  the  calories  per  liter  by  the  factor  0.11236. 

Gross  and  Net  Heating  Value.  —  A  word  of  explanation  as 
to  the  meaning  of  the  terms  gross  and  net  heating  value  may  not 
be  out  of  place.  When  a  gas  that  contains  hydrogen  or  com- 
pounds of  hydrogen  is  burned,  steam  is  formed.  If  this  steam 
at  100°  is  condensed  to  water  at  100°  within  the  heating  appara- 
tus, 537  calories  are  set  free  for  every  gram  of  water  thus  formed. 
This  amount  of  heat  thus  becomes  available  and  it,  together 
with  the  heat  liberated  upon  the  cooling  of  the  condensed  water 
to  room  temperature,  is  included  in  the  gross  heating  value  of 
the  gas. 

When,  however,  the  gas  is  used  in  gas  stoves,  gas  engines  or 
for  the  heating  of  Welsbach  mantles,  the  steam  that  is  formed 
is  not  condensed,  and  consequently  its  latent  heat  does  not  be- 
come available.  Deduction  of  this  loss  gives  the  net  heating 
value  of  the  gas. 

There  is  a  considerable  difference  of  opinion  as  to  whether 
the  gross  heating  value  or  the  net  heating  value  most  accurately 
expresses  the  calorific  power  of  the  gas.  A  discussion  of  this 
question  will  be  found  in  Stone's  Practical  Testing  of  Gas  and 
Gas  Meters. 

Automatic  Gas  Calorimeter.  —  Professor  Junkers  has  also 
devised  an  automatic  form  x  of  his  calorimeter.  The  under- 
lying principle  of  the  device  is  the  same  as  that  employed  in 
the  other  form  of  the  Junkers  apparatus,  but  the  instrument  is 
made  automatic  by  rendering  constant  the  ratio  of  the  amount 
of  gas  burned  to  that  of  water  passing  through  the  calorimeter, 
in  which  case  the  difference  of  temperature  is  a  direct  measure 
of  the  heating  value  of  the  fuel.  The  temperature  difference 
is  measured  by  a  thermocouple,  the  junctions  of  which  are 
immersed  in  the  entering  and  escaping  water.  The  readings 
are  made  on  a  millivoltmeter. 

1  J.  Gasbeleuchtung,  50  (1907),  520. 


CHAPTER  XVII 
ACETYLENE  GAS 

The  chief  object  of  the  analytical  examination  of  acetylene 
is  the  detection  and  determination  of  certain  impurities  in  the 
gas  rather  than  the  determination  of  acetylene  itself. 

Impurities  in  Commercial  Acetylene. —  Commercial  calcium 
carbide  may  be  contaminated  with  metallic  calcium,  calcium 
phosphide,  calcium  sulphide,  aluminum  carbide,  aluminum  ni- 
tride, magnesium  nitride,  or  calcium  nitride;  consequently  in  the 
analysis  of  acetylene  the  following  impurities  have  to  be  con- 
sidered, —  hydrogen,  ammonia,  phosphine,  organic  compounds 
of  phosphorus,  hydrogen  sulphide,  organic  compounds  of  sulphur, 
silicon  hydride,  carbon  monoxide,1  methane  (oxygen,  nitrogen). 

Of  these,  hydrogen,  carbon  monoxide,  methane,  oxygen,  and 
nitrogen  need  not  usually  be  determined  since  they  are,  as  a 
rule,  present  in  only  small  amounts,  are  without  appreciable 
effect  upon  the  luminosity  of  the  acetylene  flame,  arid,  if  they 
are  susceptible  of  oxidation  under  the  prevailing  conditions, 
yield  products  that  are  not  objectionable*  On  the  other  hand, 
ammonia,  phosphine,  organic  compounds  of  phosphorus,  hy- 
drogen sulphide,  organic  compounds  of  sulphur,  and  silicon 
hydride  should  be  tested  for  and,  if  found  to  be  present,  should 
be  determined,  because,  upon  combustion  of  the  gas,  nitric  acid 
is  formed  from  ammonia,  phosphoric  acid  from  phosphine  and 
other  compounds  of  phosphorus,  sulphurous  acid  and  sulphuric 
acid  from  hydrogen  sulphide  and  other  compounds  of  sulphur, 
and  silicon  dioxide  from  silicon  hydride.  These  products  of 
oxidation  vitiate  the  air  and  attack  or  clog  the  metal  parts  of 
the  burner. 

1  Keppeler,  J.  Gasbdeuchtung,  45  (1902),  804. 
355 


356  GAS  ANALYSIS 

Sampling  of  Calcium  Carbide.  —  The  analyst  may  at  times 
be  called  upon  to  analyze  acetylene  gas  itself,  but  more  often 
he  is  given  a  sample  of  calcium  carbide  and  is  asked  to  report 
upon  the  purity  of  the  acetylene  that  is  evolved  from  it.  As 
commercial  calcium  carbide  is  usually  far  from  uniform  in  com- 
position, trustworthy  results  as  to  the  purity  of  the  acetylene 
that  it  yields  can  be  obtained  only  from  an  average  sample  that 
is  prepared  from  a  fairly  large  amount  of  the  carbide.  Such  a 
sample  of  the  carbide  cannot,  however,  be  prepared  in  the  usual 
manner  by  breaking  the  lumps  into  small  pieces,  grinding  these 
to  a  powder,  and  mixing  the  powder.  The  substance  is  so 
hard  that  considerable  time  would  be  required  to  pulverize 
the  pieces,  and  during  the  work  the  moisture  of  the  air  would 
decompose  an  appreciable  amount  of  the  carbide.  The  best 
that  can  be  done  under  the  circumstances  is  to  rapidly  break 
up  the  carbide  into  pieces  about  the  size  of  a  pea,  to  sift  these 
without  delay  to  remove  the  carbide  dust,  to  then  roughly  mix 
the  pieces  of  carbide  together,  and  to  place  the  material  thus  pre- 
pared in  dry,  tightly  stoppered  bottles.  A  sample  prepared  in 
this  manner,  is,  of  course,  far  from  being  homogeneous,  and  for 
this  reason  the  portion  of  carbide  taken  for  a  determination 
should  amount  to  about  fifty,  or  even  one  hundred,  grams. 

Determination  of  Hydrogen  in  Acetylene.  —  Hydrogen  in 
crude  acetylene  results  from  the  action  of  metallic  calcium  upon 
the  water  used  to  decompose  the  calcium  carbide,  or  from 
polymerization  of  acetylene  and  splitting  off  of  hydrogen 
when  the  gas  is  generated  at  high  temperature. 

Hydrogen  in  acetylene  may  be  determined  with  the  Hempel 
apparatus  by  absorbing  the  acetylene  with  fuming  sulphuric 
acid,  oxygen  with  alkaline  pyrogallol,  the  last  traces  of  acetylene 
with  ammoniacal  cuprous  chloride,  and  determining  hydrogen 
(and  methane  if  present)  in  the  residue  by  combustion. 

Determination  of  Ammonia  in  Acetylene.  —  Ammonia  is 
formed  by  the  action  of  water  upon  metallic  nitrides,  as 
Mg3N2  +  3  H2O  =  3  MgO  +  2  NH3 


ACETYLENE  GAS  357 

Lewes  determines  ammonia  in  crude  acetylene  by  passing 
the  gas  through  a  solution  of  sulphuric  acid  of  known  strength 
and  ascertaining  the  excess  of  sulphuric  acid  by  titration  of  the 
solution  with  fo  ammonium  hydroxide,  using  litmus  as  indi- 
cator. 

Determination  of  Phosphine  in  Acetylene.  —  Phosphine  is 
almost  always  present 1  in  crude  acetylene.  It  is  due  to  the 
reaction  between  calcium  phosphide  and  water.  If  the  acetylene 
is  evolved  at  high  temperature,  as  is  frequently  the  case  when 
water  is  allowed  to  drop  upon  the  calcium  carbide,  organic  phos- 
phorus compounds  may  also  be  formed,  but  if  appreciable  rise 
of  temperature  during  the  generation  of  the  gas  is  avoided,  the 
amount  of  these  organic  substances  is  negligible,  and  all  of  the 
phosphorus  that  is  present  may  be  assumed  to  exist  in  the  form 
of  phosphine. 

The  amount  of  phosphine  in  crude  acetylene  is  quite  variable, 
but  it  usually  lies  between  .03  per  cent  and  1.8  per  cent.2  The 
regulations  of  the  British  Acetylene  Association  state  that  "  car- 
bide which,  when  properly  decomposed,  yields  acetylene  con- 
taining from  all  phosphorus  compounds  therein  more  than  0.05 
per  cent  by  volume  of  phosphine,  may  be  refused  by  the  buyer, 
and  any  carbide  found  to  contain  more  than  this  figure,  with  a 
latitude  of  .01  per  cent  for  the  analysis,  shall  lie  at  the  risk  and 
expense  of  the  seller.  ..."  If  the  permissible  maximum  of 
phosphine  lies  in  the  neighborhood  of  .05  per  cent  by  volume, 
it  is  apparent  that  the  determination  of  this  gas  in  crude  acety- 
lene cannot  satisfactorily  be  accomplished  by  a  volumetric 
absorption  method  that  uses  a  sample  of  only  one  hundred  cc. 
of  acetylene. 

Of  the  methods  that  have  been  proposed  for  the  determina- 
tion of  the  gaseous  compounds  of  phosphorus  in  acetylene,  the 

1  Vogel,  Handbuchfur  Acetylen,  p.  232. 

2  Vogel,  loc.  tit.,  p.  234.    The  analyses  given  by  Fraenkel,  /.  Gasbeleuchtung,  51 
(1908),  431,  show  from  .024  to  .057  per  cent  by  volume  of  phosphine  in  crude  acety- 
lene. 


3$8  GAS  ANALYSIS 

combustion  method  developed  by  Eitner,1  Keppeler,2  and  Fraen- 
kel,3  and  the  sodium  hypochlorite  absorption  method  of  Lunge 
and  Cedercreutz  4  are  in  most  general  use.  The  first  of  these 
methods,  in  which  the  phosphorus  in  crude  acetylene  is  deter- 
mined by  burning  the  gas  and  ascertaining  the  amount  of 
phosphoric  acid  in  the  products  of  combustion,  gives  the  total 
amount  of  phosphorus,  whether  it  is  present  in  the  gas  as  phos- 
phine  or  in  the  form  of  organic  compounds  of  phosphorus.  The 
acetylene  is  burned  in  an  Acetylene-Bunsen  burner  under  a  cylin- 
drical glass  hood,  and  the  products  of  combustion  are  drawn 
through  an  oxidizing  solution,  such  as  sodium  hypochlorite 
or  sodium  hypobromite.  The  resulting  phosphoric  acid  is  then 
determined  by  precipitation  with  "  magnesia  mixture."  On 
account  of  the  difficulty  in  regulating  the  pressure  of  the  gas  as 
it  comes  from  the  evolution  apparatus,  Fraenkel  recommends 
that  the  acetylene  from  about  50  grams  of  calcium  carbide  be 
collected  over  a  salt  solution  in  a  large  tubulated  bottle,  and 
that  the  gas  be  then  driven  from  this  bottle  through  the  burner. 
This  necessitates  the  use  of  glass  bottles  of  about  20  liters 
capacity,  and  if  the  acetylene  is  to  be  mixed  with  an  equal  vol- 
ume of  hydrogen  before  combustion,  as  Fraenkel  recommends, 
the  containers  must  be  so  large  as  to  render  them  very  unwieldy 
and  quite  expensive.  Moreover,  the  accuracy  of  the  determina- 
tion of  phosphorus  in  the  gas  will  undoubtedly  be  affected  by 
the  reaction  between  the  compounds  of  phosphorus  and  the 
confining  liquid. 

For  these  reasons  the  method  of  Lunge  and  Cedercreutz  in 
which  the  crude  acetylene  is  passed  directly  from  the  generating 
apparatus  through  a  solution  of  sodium  hypochlorite  is  to  be 
preferred  to  the  combustion  method  if  it  will  yield  accurate 
results.  The  apparatus  that  was  used  by  these  authors  is 
shown  in  Fig.  101.  A  weighed  amount  of  the  calcium  carbide 

1  /./.  Gasleleuchtung,  44  (1901),  548. 

9  Ibid.,  45  (1902),  802. 

3  Ibid.,  51  (1908),  431. 

4Z./.  angew.  Chem.,  1897,  651. 


ACETYLENE  GAS 


359 


(from  50  to  70  grams)  is  placed  in  the  flask  B,  and  there  is  in- 
serted into  the  neck  of  B  a  rubber  stopper  that  carries  a  short 
delivery  tube  and  a  separately  funnel  A.  The  ten-bulb  ab- 
sorption tube  C  is  charged  with  about  75  cc.  of  a  three  per  cent 
solution  of  sodium  hypochlorite  and  is  connected  to  the  evolu- 
tion flask.  Water  is  now  allowed  to  drop  slowly  from  A  upon 
the  carbide  in  B  at  a  rate  of  from  6  to  7  drops  a  minute.  The 
evolution  of  acetylene  will  cease  in  from  three  to  four  hours. 


FIG.  101 

Air  is  then  drawn  through  the  apparatus  to  carry  over  into  C 
any  acetylene  that  may  still  remain  in  B.  The  contents  of  the 
absorption  tube  C  is  transferred  to  a  beaker  and  the  phosphoric 
acid  in  the  solution  is  precipitated  by  magnesia  mixture. 

Objection  has  been  raised  to  this  method  because  the  acetylene 
is  generated  by  dropping  water  upon  calcium  carbide,  which 
is  said  to  give  rise  to  organic  compounds  of  phosphorus  that 
will  pass  through  the  solution  of  sodium  hypochlorite  without 
undergoing  complete  oxidation,  and  further  because  of  the  prob- 
able incompleteness  of  the  absorption  of  the  evolved  phosphine 
by  the  solution  of  sodium  hypochlorite  in  the  ten-bulb  tube. 


3<5° 


GAS  ANALYSIS 


In  seeking  to  improve  this  absorption  method  two  points  that 
present  themselves  are,  therefore, 

(1)  A  method  of  generating  acetylene  that  will  avoid  ap- 
preciable rise  of  temperature  when  the  calcium  carbide  is  de- 
composed, and 

(2)  An  absorption  apparatus  that  is  more  efficient  than  the 
ten-bulb  tube  used  by  Lunge  and  Cedercreutz. 

The  method  described  by  Dennis  and  O'Brien1  seems  to 
fulfill  these  requirements  in  a  most  satisfactory  manner. 


FIG.  i 02 

The  evolution  of  acetylene  without  marked  rise  of  temperature 
is  accomplished  in  simple  fashion  by  the  employment  of  a  small 
Kipp  apparatus  about  40  cm.  high,  and  with  bulbs  about  10  cm. 
in  diameter.  The  annular  space  around  the  stem  between  the 
middle  and  bottom  bulbs  is  covered  with  a  perforated  rubber 
disk  D  (Fig.  102).  A  solution  of  sodium  chloride,  saturated 
at  room  temperature,  is  poured  into  the  top  bulb  until  the  end 
of  the  stem  in  the  bottom  bulb  is  covered  with  the  liquid.  A 
perforated  stopper  carrying  a  short  glass  tube  is  inserted  in  the 
neck  of  the  top  bulb,  the  stopper  with  exit  tube  and  glass 

lJour.  Ind.  Eng.  Chem.,  4  (1912),  834. 


ACETYLENE   GAS  361 

stopcock  is  inserted  in  the  tubulus  of  the  bulb  B,  and  the  further 
end  of  the  outlet  tube  is  connected  with  the  absorption  appara- 
tus that  contains  the  solution  of  sodium  hypochlorite.  Hydro- 
gen gas  is  now  passed  into  the  upper  bulb  of  the  Kipp  generator 
and  through  the  absorption  apparatus  to  displace  the  air.  About 
50  grams  of  the  calcium  carbide  under  examination,  broken 
into  pieces  about  the  size  of  a  pea  and  sifted  to  remove  the  dust, 
is  placed  in  a  dry  weighing  tube  and  this  is  at  once  tightly 
stoppered  and  weighed.  When  practically  all  of  the  air  has 
been  displaced  from  the  Kipp  apparatus  by  hydrogen,  the  stop- 
per in  the  tubulus  of  the  bulb  B  is  removed,  the  contents  of  the 
sample  tube  is  poured  into  the  bulb  and  the  stopper  is  at  once 
reinserted.  The  current  of  hydrogen  through  the  apparatus 
is  continued  for  about  one  minute,  the  stopcock  is  then  closed, 
and  the  stopper  and  tube  are  removed  from  the  upper  bulb  of 
the  Kipp  generator.  An  additional  amount  of  salt  solution 
sufficient  to  cause  the  apparatus  to  function  as  a  gas  generator 
is  then  introduced  into  the  upper  bulb.  The  stopcock  is  now 
opened  to  such  an  extent  that  the  evolved  gases  pass  through 
the  apparatus  at  a  rate  slightly  faster  than  will  permit  of  the 
bubbles  being  counted.  Under  these  conditions  the  decomposi- 
tion of  a  sample  of  50  grams  will  be  effected  in  about  two  hours. 
The  reaction  between  the  salt  solution  and  the  calcium  carbide 
proceeds  at  a  uniform  rate,  and  with.no  appreciable  rise  of 
temperature. 

The  absorption  apparatus  that  is  employed  is  a  Friedrichs 
gas  washing  bottle  modified  in  form  so  that  the  apparatus  can 
easily  be  rinsed  out  with  water  at  the  close  of  the  run.  The 
absorbing  solution  is  introduced  into  the  outer  cylinder  to  such 
height  that  it  will  stand  at  the  top  of  the  widened  foot  of  the 
cylinder,  and  the  spiral  with  the  ground  glass  shoulder  is  then 
inserted.  When  a  gas  is  passed  into  the  bottle  through  the 
central  tube,  it  follows  the  grooves  of  the  spiral  when  it  rises 
and  pushes  some  of  the  solution  ahead  of  it.  These  gas  wash- 
ing bottles  are  much  more  compact  than  the  ten-bulb  tube 


362  GAS  ANALYSIS 

used  by  Lunge  and  Cedercreutz,  and  experiment  has  shown 
that  the  absorption  attained  by  their  use  is  surprisingly  rapid 
and  complete.  The  solution  of  sodium  hypochlorite  with  which 
the  absorption  apparatus  is  charged  is  prepared  by  dissolving 
15  grams  of  sodium  hydroxide  in  100  cc.  of  water,  saturating  the 
ice-cold  solution  with  chlorine,  driving  out  the  excess  of  chlorine 
with  a  current  of  air,  and  then  determining  the  amount  of  sodium 
•hypochlorite  in  the  solution  by  treatment  with  hydrogen  dioxide 
in  a  Lunge  nitrometer  (see  p.  397).  The  solution  is  then  diluted 
to  three  per  cent  NaCIO,  and  about  75  cc.  of  this  solution  is 
placed  in  each  bottle. 

After  the  decomposition  of  the  calcium  carbide  is  complete, 
the  acetylene  that  remains  in  the  generator  is  driven  over  into 
the  absorption  bottles  by  again  passing  hydrogen  through  the 
apparatus  in  the  manner  above  described.  The  contents  of  the 
gas  washing  bottles  is  transferred  to  a  beaker,  the  bottles  and 
inner  tubes  being  thoroughly  rinsed  with  distilled  water.  10  cc. 
of  concentrated  hydrochloric  acid  is  added  to  the  liquid  which 
is  then  boiled  until  the  odor  of  chlorine  is  no  longer  noticeable. 
Ammonium  hydroxide  is  added  to  alkaline  reaction  and  the 
phosphoric  acid  that  is  present  is  determined  by  precipitation 
with  magnesia  mixture,  and  weighing  as  magnesium  pyrophos- 
phate. 

The  volume  of  phosphine  to  which  the  weight  of  magnesium 
pyrophosphate  is  equivalent  may  be  calculated  as  follows  :  — 

Mg2P2O7  :  2  PH3  =  222.72  :  68.13, 
or  weight  Mg2P2O7  X  0.3059   =  weight  phosphine. 


Since  one  gram  of  phosphine  occupies  a  volume  of  657.9  cc- 
at  O°  C.  and  760  mm.  pressure, 

volume  of  PH3  in  cc.    = 
weight  in  grams  Mg2P2O7  X  0.3059  X  657.9 

or,  volume  of  PH3  in  cc.   = 

weight  in  grams  Mg2P2(>7  X  201.25 


ACETYLENE   GAS  363 

Determination  of  Volume  of  Acetylene  evolved  from  Sam- 
ple of  Carbide.  —  It  is  customary  to  report  the  results  as  the 
per  cent  by  volume  of  phosphine  in  the  evolved  acetylene.  This 
necessitates  the  determination  of  the  volume  of  gas  that  is  lib- 
erated by  the  calcium  carbide  under  examination.  The  most 
convenient  method  for  making  this  determination  is  that  pro- 
posed by  Bamberger  l  who  places  a  definite  amount  of  the  car- 
bide in  a  weighed  two-neck  Wolff  bottle  of  about  400  cc.  ca- 
pacity, and  runs  in  upon  the  carbide  an  amount  of  a  saturated 
solution  of  sodium  chloride  sufficient  to  entirely  decompose 
the  substance.  The  whole  apparatus  is  weighed  before  and  after 
the  reaction,  and  the  loss  in  weight  equals  the  weight  of  the 
evolved  gas  which  is  here  assumed  to  consist  entirely  of  acety- 
lene. The  total  weight  of  the  Bamberger  apparatus  before 
the  decomposition  of  the  carbide  amounts  to  from  550  to  800 
grams.  This  weight  may  materially  be  reduced  by  employ- 
ing, in  place  of  the  Wolff  bottle,  an  Erlenmeyer  flask  of  about 
250  cc.  capacity.  This  is  fitted  with  a  two-hole  rubber  stop- 
per into  one  opening  of  which  is  inserted  the  stem  of  a  small 
separatory  funnel  of  125  cc.  capacity;  the  other  opening  of  the 
stopper  carries  a  U-tube  filled  with  calcium  chloride.  A  sample 
of  the  calcium  carbide  amounting  to  about  50  grams  is  placed 
in  a  weighing  bottle,  is  accurately  weighed,  and  is  then  intro- 
duced into  the  flask.  The  stopper  carrying  the  separatory  fun- 
nel and  the  U-tube  is  then  inserted,  and  the  funnel  is  filled  with 
a  20  per  cent  solution  of  sodium  chloride.  The  whole  apparatus 
is  then  weighed  on  a  balance  accurate  to  o.oi  gram.  The  total 
weight  of  this  modified  form  of  the  Bamberger  device  is  approxi- 
mately 300  grams.  The  salt  solution  is  now  allowed  to  drop 
slowly  upon  the  calcium  carbide,  and,  after  decomposition  is 
complete,  dry  air  is  passed  through  the  apparatus  to  expel  all 
of  the  acetylene.  The  apparatus  is  then  again  weighed,  the 
difference  between  the  two  weighings  giving  the  weight  of  the 
acetylene  evolved.  One  kilogram  of  chemically  pure  calcium 
1  Z.f.  Cdc.  und  Acet.,  i  (1898),  210. 


364  GAS  ANALYSIS 

carbide  yields  405.93  grams  of  acetylene,  equivalent  to  348.4 
liters  of  acetylene  under  standard  conditions.  Assuming  that 
the  loss  of  weight  in  the  apparatus  equals  the  weight  of  the 
acetylene  evolved,  the  volume  of  the  liberated  gas  may  be  cal- 
culated as  follows: 

Weight  of  sample  :  Weight  C2H2  =  100  :  x, 

x  =  the  weight  of  evolved  acetylene  expressed  in  per  cent 
of  weight  of  the  calcium  carbide. 

Since  pure  calcium  carbide  will  yield  acetylene  amounting  to 
40.593  per  cent  of  the  weight  of  the  calcium  carbide, 

40.593  :  per  cent  C2H2  by  weight  =  348.4  :  x, 

x  =  the  number  of  liters  of  acetylene  evolved  from  one 
kilogram  of  the  calcium  carbide  under  examination,  or  the 
number  of  cubic  centimeters  evolved  from  one  gram  of  the  car- 
bide. 

Calculation  of  Results.  —  From  the  above  data  the  per  cent 
by  volume  of  the  phosphine  in  the  acetylene  may  now  be  cal- 
culated. An  example  of  such  a  calculation  follows : 

A.  Determination  of  Phosphine 

Calcium  carbide  taken          =  50.3548  grams. 
Weight  of  Mg2P2O7  =    0.0089  gram 

cc.  PH3  from  i  gram  CaC2  =  0.0089  X  201.25 

50-3548 

B.  Determination  of  Yield  of  Acetylene 

Calcium  carbide  taken  =  41.071  grams 
Loss  of  weight  of  apparatus  =  14.4885  grams 

41.071  :  14.4885   =  100  :  per  cent  C2H2  by  wt. 
Per  cent  C2H2  by  weight  =  35.28 

40.593:  35.28  =  348.4  :  cc.  C2H2  from  i  gram  CaC2 
Volume  C2H2  from  i  gram  CaC2  =300  cc. 


ACETYLENE  GAS  365 

Per  cent  PHs       cc.  PH3  from  i  gram  CaC2  X  100 


by  volume  cc.  CzRz  from  i  gram  CaC2 


=  0.0117  % 


To  determine  the  accuracy  of  the  results  yielded  by  this 
method,  it  was  necessary  to  ascertain 

(1)  Whether  the  gaseous  compounds  of  phosphorus  that  are 
absorbed  by  sodium  hypochlorite  would  be  entirely  taken  up  by 
two  Friedrichs  gas  washing  bottles  containing  the  reagent,  and 

(2)  Whether,  in  the  method  here  employed  for  the  generation 
of  the  acetylene,  any  gaseous  compounds  of  phosphorus  are 
evolved  that  are  not  absorbed  by  sodium  hypochlorite. 

That  complete  absorption  of  the  compounds  of  phosphorus 
is  obtained  with  only  two  of  the  gas  washing  bottles  of  the  type 
here  described,  even  when  a  sample  of  carbide  unusually  high 
in  phosphorus  was  used,  was  demonstrated  by  connecting  four 
of  the  absorption  bottles  in  series,  charging  each  with  75  cc.  of 
a  three  per  cent  solution  of  sodium  hypochlorite  and  testing 
the  contents  of  each  for  phosphoric  acid  after  the  run.  In  no 
case  was  this  acid  detectable  in  the  third  or  fourth  bottle. 

The  second  query  was  answered  in  two  ways.  The  gases  is- 
suing from  the  second  absorption  bottle  were  burned  with  an 
excess  of  oxygen,  and  the  products  of  combustion  were  found 
to  be  free  from  phosphoric  acid.  In  another  experiment  the 
crude  acetylene  from  the  generator  was"  burned  directly  with- 
out being  passed  through  the  solution  of  sodium  hypochlorite, 
and  the  result  was  found  to  agree  with  that  obtained  by  the 
absorption  method. 

The  combustion  of  acetylene  as  it  issues  from  a  bottle  con- 
taining a  liquid  absorbent  has  heretofore  presented  difficulty 
because  of  the  intermittent  flow  of  the  gas.  It  was  found,  how- 
ever, that  complete  combustion  is  easily  attained  by  passing 
the  acetylene  into  the  hydrogen  inlet  tube  of  a  Linnemann 
oxy-hydrogen  lamp,  admitting  oxygen  into  the  other  tube  of 
the  lamp,  and  insuring  continuous  combustion  by  causing  a 
small  horizontal  flame,  about  one  cm.  long,  of  illuminating  gas 


366 


GAS  ANALYSIS 


that  is  free  from  phosphorus  to  burn  across  the  orifice  of  the 
lamp. 

The  accuracy  and  uniformity  of  the  results  obtained  with  the 
method  here  described  are  shown  in  the  following  tabulation 
of  analyses  by  the  absorption  method,  and  by  the  method  of 
combustion. 

TABLE  A 

This  sample  CaC2  yielded  300  liters  C2H2  per  kilogram 


No. 

Weight  of 
sample  in 
grams 

Weight  of 

Mg2P2O7 

in  grams 

PER  CENT  OF  PHOSPHINE  IN 
EVOLVED  ACETYLENE 

byNaCIO 
method 

by  combustion 
method 

I 

2 

3 
4 

6 

8 

9 
10 
ii 

50.3548 
50-3572 
50.  1870 
50.3027 
50  .  0036 
50  -  3047 
50.1625 
50  .  oooo 
50  .  oooo 
50  .  oooo 
50.0612 

.0089 
.0073 
.0062 
.0050 
.0062 
.0059 
•0059 
.0072 
.0047 
.0060 
.0062 

.0117 
.0097 
.0083 
.0066 
.0083 
.0078 
.0078 

.0096 
.0063 
.0080 
.0083 

Average 

.0086 

.0080 

TABLE  B 

This  sample  CaC2  yielded  287  liters  C2H2  per  kilogram 


No. 

Weight  of 
sample  in 
grams 

Weight  of 
Mg2P207 
in  grams 

PER  CENT  OF  PHOSPHINE  IN 
EVOLVED  ACETYLENE 

byNaCIO 
method 

by  combustion 
method 

I 

2 

3 

4 

6 

7 
8 

50.0651 
50.0200 
50.0432 
50.1004 
50  .  0600 
50.1043 
50.0612 
50.0121 

.0661 
.0592 
.0782 
.0582 
.0680 
.0641 
.0601 
.0642 

.0925 
.0829 
.1093 
.0814 

.0948 
.0896     . 
.0841 
.0899 

Average 

.0915 

.0896 

ACETYLENE   GAS  367 

The  results  given  in  Table  A  were  obtained  with  a  sample 
of  commercial  calcium  carbide.  To  ascertain  whether  the 
method  would  give  uniform  results  when  the  acetylene  con- 
tained a  relatively  large  amount  of  phosphine,  a  sample  of 
calcium  carbide  high  in  phosphorus  was  prepared,  and  the 
analyses  of  this  product  by  the  two  methods  are  given  in 
Table  B. 

Determination  of  Sulphur  in  Acetylene.  —  The  source  of 
hydrogen  sulphide  in  crude  acetylene  has  been  the  subject  of 
considerable  discussion.  It  is  commonly  thought  to  be  the 
calcium  sulphide  that  is  formed  when  the  raw  material  from 
which  the  calcium  carbide  is  prepared  contains  gypsum.  But 
Moissan  showed l  that  the  product  resulting  from  heating  gyp- 
sum and  carbon  in  an  electric  furnace  gave  with  cold  water  an 
acetylene  free  from  hydrogen  sulphide,  and  moreover  that  the 
water  used  in  the  reaction  after  the  residue  had  been  removed 
by  filtration  gave  no  reaction  for  hydrogen  sulphide.  He  there- 
fore attributed  the  presence  of  hydrogen  sulphide  in  crude 
acetylene  to  aluminum  sulphide,  which  is  easily  decomposed 
by  water  with  liberation  of  hydrogen  sulphide. 

In  contradiction  of  this  assumption,  Wolff 2  found  that  samples 
of  calcium  carbide  entirely  free  from  aluminum  liberated  hy- 
drogen sulphide  when  treated  with  water.  When  acetylene  is 
set  free  from  calcium  carbide  in  such  manner  as  to  avoid  ap- 
preciable rise  in  temperature,  the  evolved  gas  seldom  contains 
hydrogen  sulphide.  It  is  known,  however,  that  when  calcium 
sulphide  lies  in  contact  with  water  for  a  considerable  time,  it 
changes  to  a  soluble  primary  sulphide.  It  is  reasonable  to  sup- 
pose that  this  change  will  take  place  more  rapidly  at  high  tem- 
peratures, and  consequently  when  acetylene  is  set  free  by  drop- 
ping water  upon  the  carbide,  hydrogen  sulphide  may  result 
from  the  action  of  the  water  upon  calcium  sulphide.  Moreover, 
Lunge  and  Cedercreutz  found  that  crude  acetylene  contains 

1  Compt.  rend.,  1898,  457. 

2Z./.  Cole,  und  Acet.,  I  (1898),  272. 


368  GAS  ANALYSIS 

sulphur  in  a  form  not  precipitable  by  lead  acetate  which  indi- 
cated that  the  sulphur  in  the  gas  was  in  the  form  of  organic 
compounds  of  the  element.  Caro  considers l  that  these  volatile 
organic  sulphur  compounds  do  not  exist  in  the  carbide,  but  are 
secondary  products  resulting  from  the  action  of  hydrogen  sul- 
phide upon  acetylene.  Whatever  their  source  may  be,  it  is  a 
fact  that  crude  acetylene  contains  at  times  hydrogen  sulphide 
and  volatile  organic  compounds  of  sulphur,  and  consequently 
these  substances  must  be  taken  into  consideration  in  a  complete 
analysis  of  the  crude  gas. 

The  determination  of  sulphur  in  acetylene  may  conven- 
iently be  combined  with  the  determination  of  phosphine  (see 
under  Phosphine,  p.  360).  The  sodium  hypochlorite  solution 
oxidizes  compounds  of  sulphur  to  sulphuric  acid.  Phosphoric 
acid  that  is  simultaneously  formed  is  precipitated  by  magnesia 
mixture  that  is  free  from  sulphates.  After  the  ammonium 
magnesium  phosphate  precipitate  has  been  removed  by  filtra- 
tion, the  filtrate  is  acidified  with  hydrochloric  acid,  heated 
nearly  to  boiling,  and  the  sulphuric  acid  precipitated  with  ba- 
rium chloride.  It  has  been  claimed  by  some  that  this  method 
does  not  oxidize  all  of  the  sulphur  compounds  in  the  gas,  and 
that  accurate  results  will  be  obtained  only  when  the  crude  acety- 
lene is  burned  and  the  sulphuric  acid  is  determined  in  the  com- 
bustion products. 

Determination  of  Silicon  Hydride  in  Acetylene.  —  There 
is  considerable  difference  of  opinion  as  to  whether  this  gas  is 
present  in  acetylene.  The  work  of  Lewes  and  of  Fraenkel  ap- 
pears to  demonstrate  its  existence  in  certain  samples  of  crude 
acetylene  although  the  amounts  that  they  found  were  quite 
small,  about  o.oi  per  cent  by  volume  or  ten  cc.  in  100  liters. 
The  gas  may  be  determined  by  the  method  used  by  Fraenkel 2 
which  consists  in  burning  crude  acetylene  under  a  cylinder  of 
glass,  or  better  of  platinum,  rinsing  out  the  cylinder  with  hy- 

1  Z.f.  Cole,  und  Acet.,  i  (1898),  337- 

2  J.f.  Gasbeleuchtung,  51  (1908),  433. 


ACETYLENE  GAS  369 

drochloric  acid  and  determining  the  silica  that  has  resulted 
from  the  combustion. 

Determination  of  Carbon  Monoxide  in  Acetylene. —  Kep- 
peler  1  believes  that  crude  acetylene  contains  a  small  amount 
of  carbon  monoxide  and  bases  his  belief  upon  the  fact  that  after 
he  had  absorbed  the  acetylene  by  fuming  sulphuric  acid  in  a 
Hempel  pipette  and  had  treated  the  gas  residue  with  potassium 
hydroxide,  bromine  and  phosphorus,  there  was  further  ab- 
sorption when  the  residual  gas  was  passing  into  a  pipette  con- 
taining a  solution  of  cuprous  chloride.  Assuming  that  this 
absorption  was  due  entirely  to  carbon  monoxide,  he  found  that 
the  amount  of  that  gas  was  about  0.02  per  cent  of  the  crude 
acetylene. 

Lundstrom,2  however,  found  as  much  as  1.48  per  cent  of 
carbon  monoxide  in  acetylene,  and  Caro  as  high  as  2.3  per  cent. 
The  source  of  the  carbon  monoxide  is  still  in  doubt. 

Determination  of  Methane  in  Acetylene. —  From  the  work 
of  Rossel  and  Sandriset 3  and  of  v.  Knorre  and  Arndt,4  it  would 
appear  that  there  is  no  methane  in  acetylene  that  has  been 
properly  generated.  If,  however,  the  gas  is  evolved  at  high 
temperature,  it  may  contain  considerable  amounts  of  methane.5 
The  gas  may  be  determined,  together  with  any  hydrogen  that 
may  be  present  in  the  acetylene,  by  combustion  of  the  non- 
absorbable  residue  (see  under  Hydrogen,  p.  356). 

Determination  of  Oxygen  and  Nitrogen  in  Acetylene.  — 
Oxygen  and  nitrogen  may  be  determined  volumetrically  by 
the  procedure  described  under  hydrogen,  p.  356,  the  nitrogen 
being  the  gas  that  remains  after  the  determination  of  hydrogen 
and  methane. 

lJ.f.  Gasbekuchiung,  45  (1902),  802. 

2  Chemiker-Zeitung,  23  (1899),  180. 

3  Z./.  angew.  Chem.,  1901,  77. 

4  Z.  d.  Ver.  2.  Forderg.  d.  Gewerbefleisses,  1900,  162. 
6  Lewes,  /.  Soc.  Chem.  Ind.,  17  (1898),  533. 


CHAPTER  XVIII 
EXAMINATION  OF  ATMOSPHERIC  AIR 

Composition  of  Atmospheric  Air.  —  The  normal  constitu- 
ents of  the  atmosphere  are  nitrogen,  oxygen,  the  gases  of  the 
argon  group,  carbon  dioxide  and  water  vapor.  These  substances, 
with  the  exception  of  water  vapor,  are  present  in  nearly  con- 
stant amount  in  air  that  is  free  from  local  contamination. 

Nitrogen 78 .  i    per  cent  by  volume 

Oxygen 20.94 

Carbon  Dioxide      .      .      .       0.03 


Argon     . 
Neon 
Helium  . 
Krypton 
Xenon    . 


volume  in  106 . 8  volumes  of  air 

80,800 
245,300 
"        "     20,000000 

"  170,000,000  " 


Local  conditions  may,  however,  give  rise  to  the  presence  in  air  of 
such  substances  as  ammonia,  nitrous  acid,  nitric  acid,  sulphur 
dioxide,  sulphuric  acid,  carbon  monoxide,  soot,  ozone,1  etc.  The 
possibility  of  the  presence  of  these  and  other  occasional  constit- 
uents in  the  atmosphere  renders  it  necessary  to  adopt  such 
methods  in  the  examination  of  air  as  will  meet  the  demands  of  the 
special  case  in  hand.  The  determination  of  most  of  the  sub- 
stances enumerated  above  is  discussed  in  Chapter  XIII.  Two 
constituents,  however,  water  vapor  and  carbon  dioxide,  deserve 
special  consideration  because  almost  every  examination  of  air 
from  a  sanitary  standpoint  involves  the  determination  of  these 
two  substances.  Many  methods  for  rapidly  and  accurately  de- 
termining these  constituents  of  the  atmosphere  have  been  de- 

1  See  p.  178. 


EXAMINATION  OF  ATMOSPHERIC  AIR          371 

veloped,  and  a  few  of  the  more  satisfactory  procedures  thus  far 
devised  will  here  be  described. 

A  very  complete  discussion  of  the  history  of  air  analysis,  and 
of  the  amounts  of  oxygen  and  carbon  dioxide  in  the  atmosphere 
has  recently  appeared  from  the  pen  of  F.  G.  Benedict.1 

DETERMINATION  OF  MOISTURE  IN  THE  ATMOSPHERE 

Absolute  and  Relative  Humidity.  —  Water  vapor  is  always 
present  in  atmospheric  air,  but  the  amount  varies  greatly. 
The  maximum  quantity  of  water  vapor  that  can  be  present  in 
any  given  space  is  dependent  upon  the  prevailing  temperature 
but  is  independent  of  the  amount  of  air  in  that  space.  When 
this  maximum  quantity  of  water  vapor  is  present,  the  space 
is  said  to  be  saturated  with  water  vapor.  The  quantity  of  water 
vapor  existent  in  a  given  space,  such  as  a  cubic  foot  or  a  cubic 
meter,  is  termed  the  "  absolute  humidity"  and  may  be  expressed 
in  terms  of  its  weight  (in  grains  or  grams)  or  of  its  pressure 
(in  inches  or  millimeters  of  mercury).  The  ratio  between  the 
amount  of  water  vapor  actually  present  in  a  given  space  and 
the  maximum  quantity  of  the  vapor  that  could  exist  in  that 
space  at  the  observed  temperature  is  termed  the  "relative 
humidity."  It  is  usually  expressed  in  per  cent  of  the  maximum 
humidity. 

Wet  and  Dry  Bulb  Thermometers.  —  Of  the  large  number 
of  methods  that  have  been  devised  for  the  determination  of  the 
amount  of  water  vapor  in  air,  one  of  the  most  satisfactory  is 
that  employed  by  the  Weather  Bureau  of  the  United  States 
Department  of  Agriculture.  It  is  based  upon  the  facts  that 
water  will  evaporate  as  long  as  the  adjacent  space  is  not  satu- 
rated with  water  vapor,  and  that  this  evaporation  is  accompanied 
by  the  absorption  of  heat.  Consequently,  if  two  thermometers 
are  exposed  to  the  air  and  a  moist  cloth  is  placed  around  the 
bulb  of  one  of  them,  this  "wet  bulb"  thermometer  will  show  a 

1  The  Composition  of  the  Atmosphere.  Publication  No.  166  of  the  Carnegie  Institu- 
tion of  Washington,  1912. 


372 


GAS  ANALYSIS 


lower  temperature  than  the  "dry  bulb"  thermometer  unless  the 
surrounding  space  is  saturated  with  water  vapor.  The  less  the 
amount  of  moisture  in  the  air,  the  greater  will  be  the  drop  in 
temperature  of  the  wet-bulb  thermometer.  From  the  final 


FIG.  103 

readings  of  the  two  thermometers  the  amount  of  water  vapor 
then  present  in  the  air  may  be  calculated. 

The  Whirling  Psychrometer.  —  The  instrument  employed 
by  the  Weather  Bureau  for  this  work  is  termed  the  whirling 
psychrometer.  Fig.  103.  It  consists  of  two  thermometers  A  and  B 


EXAMINATION  OF  ATMOSPHERIC  AIR  373 

which  are  mounted  upon  arms  that  can  be  whirled  by  turning 
the  handle  C.  The  bulb  of  one  thermometer  (the  "wet  bulb") 
is  covered  with  a  piece  of  thin  muslin  that  should  first  be  washed 
to  remove  sizing.  A  small  rectanglar  piece  of  the  washed  mus- 
lin, wide  enough  to  go  about  one  and  one-third  times  around  the 
bulb,  and  long  enough  to  cover  the  bulb  and  a  part  of  the  stem 
above  the  bulb,  is  thoroughly  moistened  with  distilled  water 
and  is  neatly  fitted  around  the  thermometer.  It  is  first  tied 
around  the  upper  end  with  a  piece  of  strong  thread.  A  loop 
of  thread  is  next  passed  around  the  lower  end  where  it  projects 
beyond  the  bulb,  and  the  thread  is  then  drawn  tightly  around 
the  muslin  in  a  knot  close  up  to  the  lower  surface  of  the  bulb 
and  the  knot  is  secured.  If  this  is  properly  done  the  muslin  will 
be  neatly  stretched  over  the  bulb  and  securely  fastened  at  the 
bottom.1 

Manipulation  of  the  Whirling  Psychrometer. —  In  making 
a  determination  of  atmospheric  moisture  the  "wet  bulb"  is 
dipped  into  a  cup  of  pure  water  to  thoroughly  saturate  the  mus- 
lin with  water.  The  handle  C  is  then  turned  and  the  thermome- 
ters are  rapidly  whirled  for  from  fifteen  to  twenty  seconds.  The 
whirling  is  stopped,  and  the  two  thermometers  are  quickly 
read,  the  "wet  bulb"  thermometer  being  first  read.  They  are 
immediately  whirled  again  and  a  second  reading  is  taken.  This 
is  repeated  until  two  successive  readings  of  the  "wet  bulb" 
agree  very  closely,  which  shows  that  the  thermometer  has 
reached  its  lowest  temperature.  The  thermometers  must  usually 
be  whirled  a  minute  or  more  before  this  temperature  is  reached. 

The  rate  of  evaporation  of  the  water  surrounding  the  "wet 
bulb"  will  vary  as  the  movement  of  the  air  past  the  bulb  varies, 
and  for  these  reasons  accurate  results  cannot  be  obtained  un- 
less the  speed  of  passage  of  the  air  by  the  bulb  is  rapid  and  uni- 
form. It  is  for  this  reason  that  the  thermometers  are  whirled. 
The  whirling  should  not  be  too  fast,  but  should  be  carried  on 
at  such  rate  that  the  bulb  of  the  thermometer  will  have  a  veloc- 

1  See  U.  S.  Dept.  of  Agriculture,  Weather  Bureau,  Bulletin  No.  235,  p.  5. 


374  GAS  ANALYSIS 

ity  of  about  fifteen  feet  per  second,  which  with  the  above  in- 
strument will  be  obtained  by  turning  the  handle  C  about  one 
and  one-half  revolutions  per  second. 

Calculation  of  Results.  —  In  the  calculation  of  results  the 
following  equation  is  employed: 

e  =  e 


0.000367  P  (t  —  0  (i  + 


in  which  e  is  the  absolute  humidity  in  inches  of  mercury,  /  and  /' 
are  the  temperatures  respectively  of  the  "dry"  and  "wet  bulb" 
thermometers  expressed  in  degrees  Fahrenheit,  P  is  the  baro- 
metric pressure  of  the  air  in  inches  of  mercury  and  e'  is  the  maxi- 
mum tension  of  water  vapor  in  inches  of  mercury  at  the  tem- 
perature /'  of  the  "wet  bulb.  " 

The  relative  humidity  may  then  be  calculated  with  the  aid 
of  the  tables  given  in  the  bulletin  of  the  Weather  Bureau  cited 
above. 

It  would  seem  preferable,  in  scientific  work,  to  express  the 
temperatures  in  degrees  Centigrade,  and  the  barometric  pres- 
sure in  millimeters  of  mercury.  If  this  be  done  the  formula  be- 
comes 

(873  +  0 


e  =  e'  —  .000661  B(t  —  0 


873 


in  which  B  is  the  barometric  pressure  in  millimeters  of  mercury, 
and  /  and  tf  are  the  temperatures  of  the  wet  and  dry  bulb  ther- 
mometers in  degrees  Centigrade. 

The  absolute  humidity  e  having  thus  been  ascertained,  the 
relative  humidity  is  calculated  by  dividing  this  result  by  the  maxi- 
mum tension  of  water  vapor  E  possible  at  the  temperature 
shown  by  the  dry  bulb  thermometer.  This  result  multiplied 
by  100  gives  the  relative  humidity  expressed  in  "degrees"  or 
per  cent. 

Relative  humidity  in         e 

=  -  X  ioo 
degrees  or  per  cent  _g 


EXAMINATION  OF  ATMOSPHERIC   AIR  375 

The  values  of  E  at  temperatures  between  —  2°  C.  and  +  34°  C. 
will  be  found  on  p.  41 1. 

The  August  Psychrometer. — A  somewhat  simpler  instrument 
than  the  whirling  psychrometer  but  one  that  is  based  upon  the 
same  principle  is  the  August  Psychrometer.  It  consists  of  two 
thermometers  placed  side  by  side  on  a  stand.  The  bulb  of  one 
of  the  thermometers  is  covered  with  thin  muslin  that  is  kept 
moist  by  a  small  lamp-wick  which  is  fastened  over  the  muslin  and 
dips  into  a  vessel  that  contains  water.  Evaporation  is  allowed  to 
proceed  until  the  temperature  of  the  wet  bulb  ceases  to  fall. 
The  temperature  of  this  thermometer,  /  ,  is  then  read,  and  also 
that  of  the  dry  thermometer,  /.  The  absolute  humidity  of  the 
air  is  then  calculated  with  the  use  of  the  formula  — 

e  =  e  —k(t  —  t'}b 

in  which  e  is  the  tension  corresponding  to  the  temperature  /', 
and  b  is  the  barometric  pressure  in  millimeters,  k  is  an  empirical 
factor  that  varies  with  the  speed  of  flow  of  the  air  past  the  wet 
bulb.  According  to  the  researches  of  Regnault,  the  values  for  k 
under  different  conditions  are  as  follows :  — 

In   small  closed  rooms o .  ooi  28 

"    large      "  "       .      . o.ooioo 

"  halls  with  open  windows     .      .      .      .      .      .  0.00077 

"  courts       .      .      .      .      .      .      .      .  •  .      .      .  0.00074 

'    open  air  (no  wind) o .  00090 

It  is  not  always  easy,  however,  to  decide  which  factor  should  be 
used,  and  experience  has  shown  that  the  August  psychrometer 
will  yield  satisfactory  results  only  when  it  is  standardized  against 
the  whirling  psychrometer,  and  the  proper  factor  for  the  special 
surroundings  is  thus  determined. 

The  Hygrodeik.  —  There  is  obtainable  on  the  market  a  con- 
venient modification  of  the  August  psychrometer  that  is  termed 
Lloyd's  Hygrodeik.  By  means  of  a  pointer  and  chart  attached 
to  this  instrument,  the  relative  humidity  of  the  atmosphere 
may  be  read  off  with  ease  and  celerity. 


376  GAS  ANALYSIS 


Determination  of  Carbon  Dioxide  in  the  Atmosphere 

The  deleterious  effects  that  result  from  the  breathing  of  air 
in  crowded  or  ill-ventilated  rooms  have,  until  quite  recently, 
been  supposed  to  be  due  to  poisonous  substances  exhaled  from 
the  lungs  of  the  occupants.  Inasmuch  as  it  has  been  impossible 
to  ascertain  the  quantity  of  these  emanations  from  the  lungs, 
the  carbon  dioxide,  which  is  simultaneously  exhaled  and  which 
can  be  accurately  determined,  has  been  regarded  as  a  measure 
of  the  toxic  organic  substances. 

The  theory  is  now  advanced  that  the  injurious  effects  arising 
from  poor  ventilation  are  due  not  to  toxic  emanations  from  the 
lungs,  but  rather  "to  a  disturbance  of  the  normal  thermal 
relations  of  the  body.  It  is  a  common  observation  that  the 
depression  and  fatigue  experienced  on  a  hot,  humid  August 
day  are  very  similar  to  the  feelings  that  develop  in  a  crowded 
' close'  room.  The  cause  is  apparently  the  same  in  both  cases, 
namely,  interference  with  the  normal  rate  of  loss  of  body  heat. 
At  least  three  atmospheric  factors  may  be  concerned  in  such 
interference:  high  temperature  of  the  ambient  air,  high  mois- 
ture content  and  lack  of  air  movement.  Paul l  kept  healthy 
persons  for  several  hours  in  a  close  cabinet  until  the  carbon 
dioxide  rose  to  100  or  150  parts  per  thousand  —  more  than 
ten  times  the  amount  usually  stated  as  t  allowable '  —  but  so 
long  as  the  temperature  and  moisture  content  were  kept  low, 
no  symptoms  of  illness  or  discomfort  developed.  Other  experi- 
menters have  reached  the  same  result  by  simply  having  electric 
fans  whirled  in  such  an  experiment  cabinet.  The  motion  these 
imparted  to  the  air  was  sufficient  to  facilitate  a  normal,  physio- 
logic loss  of  heat  from  the  body  in  spite  of  high  temperature 
and  humidity.  Similar  cabinet  experiments  in  which  the  sub- 
ject was  enabled  to  breathe  the  fresh  outside  air  through  a  tube, 
but  was  otherwise  subjected  to  the  conditions  of  a  close  room, 

1  Paul,  Ztschr.f.  Hyg.,  49  (1905),  405. 


EXAMINATION  OF  ATMOSPHERIC  AIR          377 

likewise  showed  that  the  symptoms  attributed  to  'bad  ventila- 
tion '  are  in  nowise  due  to  poisons  excreted  in  the  breath.  The 
upshot  of  all  such  experiments  is  that  it  is  not  the  chemical 
constitution  of  indoor  air  that  is  injurious,  but  the  overheating, 
the  stagnation  and  sometimes  the  moisture  content."1 

Even  if  this  view  were  correct,  it  still  remains  true  that  the 
amount  of  carbon  dioxide  in  the  air  of  a  room  furnishes  a  means 
of  judging  the  efficiency  of  the  ventilation,  and  for  this  rea- 
son the  accurate  determination  of  this  constituent  is  still  of 
importance  even  although  it  should  appear  that  the  accompany- 
ing exhaled  products  from  the  lungs  are  not  toxic  in  character. 

According  to  Benedict  2  the  amount  of  carbon  dioxide  in 
air  serves  as  quite  an  exact  indication  of  the  per  cent  of  oxygen 
that  is  present.  "For  every  o.oi  per  cent  increase  in  the  at- 
mospheric carbon  dioxide,  one  may  safely  assume  a  correspond- 
ing decrease  in  the  percentage  of  oxygen." 

Methods  employed  in  Determination  of  Carbon  Dioxide  in 
Air.  —  The  methods  that  have  been  devised  for  the  determina- 
tion of  carbon  dioxide  in  the  atmosphere  may  roughly  be  divided 
into  two  classes  —  those  in  which  the  carbon  dioxide  is  ab- 
sorbed by  a  suitable  solution  of  known  strength,  and  the  excess 
of  the  absorbent  is  determined  by  chemical  means,  and  those  in 
which  the  carbon  dioxide  is  absorbed  and  the  consequent  de- 
crease in  the  volume  of  the  sample  of  air  is  measured. 

The  Hesse  Method.  —  A  great  number  of  methods  of  the 
first  class  have  been  proposed.  Most  of  them  aim  to  give  ap- 
proximate results  in  a  short  space  of  time.  These  will  not  here 
be  considered.  Of  the  other  and  more  accurate  methods,  that 
original  with  Saussure  and  improved  by  Pettenkofer  and  later 
by  Hesse  3  has  proven  itself  to  be  one  of  the  most  satisfactory. 

1  Jour.  Amer.  Med.  Association,  September  16,  1911,  Vol.  57,  No.  12,  p.  980. 

2  The  Composition  of  the  Atmosphere.    Publication  No.  166  of  the  Carnegie  Institu- 
tion of  Washington,  1912,  p.  115. 

3  Anleitung  zur  Bestimmitng  der  Kohlensaure  in  der  Luff,  nebst  einer  Beschreibung 
des  hierzu  nothigen  Apparates;  Eulenberg's  Vierteljahrsschr.  f.  gerichtl.  Medicin  und 
ojfentl.  Sanitatswesen,  N.  F.  31,  2. 


378 


GAS  ANALYSIS 


In  this  procedure  the  carbon  dioxide  in  a  known  volume  of 
air  is  absorbed  by  a  solution  of  barium  hydroxide  of  known 
strength  and  the  amount  of  barium  hydroxide  that  has  not 
combined  with  carbon  dioxide  is  then  determined  oy  titration 
with  a  solution  of  oxalic  acid,  phenolphthaleiri  being  used  as 
indicator. 

Solutions  used  in  the  Hesse  Method. — The  stock  solutions 
needed  in  the  analysis  are  the  following  — 

(i)  One  kilogram  of  barium  hydroxide  and  50  grams  of  barium 
chloride  are  added  to  about  five  liters  of  distilled  water  con- 
tained in  a  large  bottle.  As  the  clear  supernatant  liquid  is 
used,  it  is  replaced  by  water  so  long  as  there  is  solid  material 
in  excess. 

(2)  A  dilute  solution  of  barium 
hydroxide  that  is  prepared  by 
adding  about  30  cc.  of  the  con- 
centrated solution  No.  i  to  one 
liter  of  water.  This  is  placed  in 
a  bottle  B  (Fig.  104),  provided 
with  a  small  absorption  bottle  C 
that  contains  potassium  hydrox- 
ide which  frees  the  entering  air 
from  carbon  dioxide.  This  dilute 
solution  may  also  be  prepared 
directly  by  dissolving  1.7  grams 
of  a  mixture  of  barium  hydroxide 
and  barium  chloride  (20:1)  in  one 
liter  of  distilled  water.  Phenol- 

phthalein  is  added  to  this  solution  until  it  has  a  faint  but  dis- 
tinct pink  color. 

(3)  A  solution  of  oxalic  acid  that  contains  5.6325  grams  of 
crystallized  oxalic  acid  in  one  liter  of  water.    One  cc.  of  this 
solution  is  equivalent  to  one  cc.  of  carbon  dioxide. 

(4)  A  solution  of  phenolphthalein  that  contains  one  part 
of  the  substance  dissolved  in  250  parts  of  alcohol. 


FIG.  104 


EXAMINATION  OF  ATMOSPHERIC  AIR  379 

Collection  of  Samples  of  Air.  —  The  samples  of  air  are  col- 
lected in  thick- walled  Erlenmeyer  flasks  of  100,  200,  300,'  400, 
500  cc.  capacity  that  are  supplied  with  tightly  fitting,  double- 
bore  rubber  stoppers.  The  point  to  which  the  rubber  stopper 
reaches  into  the  neck  of  the  flask  is  marked  on  each  flask,  and 
the  capacity  of  the  flask  up  to  this  line  is  determined  and  is 
marked  on  the  glass.  Pieces  of  glass  rod  from  3  to  5  cm.  long  are 
used  to  close  the  openings  in  the  stoppers.  These  rods  should 
be  well  rounded  at  the  lower  ends  and  should  be  widened  at  the 
upper  end  by  heating  them  in  the  flame  of  a  blast  lamp  and 
pressing  them  on  a  cold  surface.  Further  apparatus  that  is 
needed  in  the  work  comprises  a  pipette  of  10  cc.  capacity,  and 
a  burette  with  glass  stopcock.  The  burette  has  a  capacity  of 

from  10  to  15  cc.,  is  graduated  in  —  cc.,  and  has  a  tip  about 

8  cm.  long. 

Manipulation.  —  Each  determination  of  carbon  dioxide  by 
Hesse's  method  is  in  reality  a  double  one,  two  determinations 
of  the  constituent  being  made  in  samples  of  air  of  different  vol- 
umes. These  samples  are  collected  in  two  of  the  Erlenmeyer 
flasks  above  described,  the  two  flasks  being  of  different  capacity 
and  the  sizes  of  the  flasks  that  are  used  depending  upon  whether 
a  smaller  or  a  larger  amount  of  carbon  dioxide  in  the  air  is  to  be 
expected.  The  samples  of  air  are  collected  by  completely  filling 
the  flasks,  at  the  place  where  the  air  is  to  be  examined,  with  dis- 
tilled water  that  has  the  same  temperature  as  the  surrounding 
air,  and  then  pouring  out  the  water  and  immediately  inserting 
the  rubber  stoppers  in  the  necks  of  the  flasks,  the  holes  of  the 
stoppers  being  closed  with  the  glass  plugs.  In  this  operation  care 
should  be  exercised  that  the  flask  is  not  warmed  by  the  hand  and 
that  no  air  exhaled  by  the  operator  enters  the  flask.  The  flasks 
are  transferred  to  the  laboratory  and  the  carbon  dioxide  in 
each  of  the  two  samples  is  then  determined.  The  glass  plug  is 
removed  from  the  end  of  the  rubber  tube  (Fig.  104),  the  tip 
of  the  10  cc.  pipette  is  inserted  into  the  end  of  the  tube,  the 


380  GAS  ANALYSIS 

pinchcock  is  opened  and  some  of  the  solution  of  barium  hy- 
droxide is  drawn  up  into  the  pipette.  The  pipette  is  rinsed  with 
this  solution  which  is  then  driven  out  of  the  pipette.  The  pipette 
is  then  reinserted  in  the  end  of  the  rubber  tube  and  barium  hy- 
droxide is  drawn  up  to  the  zero  mark  whereupon  the  pinchcock 
is  closed.  One  of  the  glass  plugs  in  the  stopper  of  one  of  the 
Erlenmeyer  sample  flasks  is  withdrawn  and  the  tip  of  the  pi- 
pette is  inserted  into  the  flask  through  this  opening.  The  solu- 
tion of  barium  hydroxide  is  then  run  into  the  flask,  the  air  that 
is  displaced  by  the  solution  being  allowed  to  escape  by  moment- 
arily removing  the  glass  plug  in  the  other  hole  of  the  stopper. 
The  last  drops  of  barium  hydroxide  in  the  pipette  are  driven  out 
by  closing  the  upper  end  of  the  pipette  with  the  finger,  and 
warming  the  wider  portion  of  the  pipette  with  the  hand.  The 
pipette  is  then  withdrawn  from  the  flask  and  the  stopper  is 
closed  with  the  glass  plug.  This  procedure  is  repeated  with 
the  other  sample  of  air  contained  in  the  second  flask.  The 
closed  flasks  are  allowed  to  stand  for  from  fifteen  to  twenty 
minutes  with  occasional  shaking.  For  the  complete  absorption 
of  the  carbon  dioxide  in  the  sample  of  air  in  the  flask  it  is  essen- 
tial that  the  barium  hydroxide  be  present  in  so  large  excess  that 
not  more  than  one-fifth  of  it  enters  into  the  reaction.  If  the 
sample  of  air  is  quite  large,  or  if  the  carbon  dioxide  contained 
is  high,  20  or  even  25  cc.  of  the  solution  of  barium  hydroxide 
should  be  used. 

While  the  absorption  of  carbon  dioxide  in  the  flask  is  pro- 
ceeding, the  strength  of  the  solution  of  barium  hydroxide  is 
determined  by  filling  the  burette  to  the  mark  with  the  dilute, 
standardized  solution  of  oxalic  acid  (0.56325  gram  per  liter), 
inserting  the  tip  of  the  burette  through  one  opening  of  a 
two-hole  rubber  stopper,  placing  the  stopper  in  the  neck  of  a 
100  cc.  Erlenmeyer  flask  in  the  manner  shown  in  Fig.  105, 
and  then  running  into  the  flask  a  volume  of  the  solution 
of  oxalic  acid  almost  sufficient  to  neutralize  10  cc.  of  the  solu- 
tion of  barium  hydroxide.  10  cc.  of  this  latter  solution  is 


EXAMINATION  OF  ATMOSPHERIC  AIR 


38! 


then  introduced  into  the  flask  in  the  manner  above  described 
and  the  oxalic  acid  is  then  carefully  added  until  the  pink  color 
of  the  indicator  just  disappears.  This  color  will  frequently 
reappear  on  standing  because  of  the  presence  of  traces  of 
potassium  hydroxide  or  sodium  hy- 
droxide in  the  solution. 

The  excess  of  barium  hydroxide  in 
the  two  sample  flasks  is  then  titrated 
by  filling  the  burette  to  the  mark 
with  the  standardized,  dilute  oxalic 
acid,  inserting  the  tip  of  the  burette 
through  one  of  the  openings  of  the 
stopper  and  running  in  the  oxalic 
acid  at  first  rapidly,  and  then  to- 
ward the  end  of  the  reaction  drop 
by  drop.  The  increase  of  pressure  in 
the  flask  is  relieved  from  time  to 
time  by  momentarily  lifting  the  glass 
plug  in  the  other  opening  of  the 
stopper.  As  before,  the  end  point  of 
the  reaction  is  the  first  disappearance 
of  the  pink  color. 

Calculation    of    Results.  —  The 
temperature   and  the  prevailing  at-  — — 
mospheric    pressure   are    then   read.  FIG.  105 

10  cc.  is  deducted  from  the  volume  of 

each  sample  flask  to  allow  for  the  volume  of  air  displaced  by 
the  solution  of  barium  hydroxide  that  has  been  introduced, 
and  the  remaining  volume  is  corrected  to  standard  conditions 
of  temperature  and  pressure.  This  result  represents  the  vol- 
ume of  the  air  sample  in  the  flask.  The  number  of  cubic  cen- 
timeters of  the  solution  of  oxalic  acid  required  to  neutralize 
the  excess  of  the  barium  hydroxide  is  deducted  from  the  volume 
of  oxalic  acid  required  to  neutralize  10  cc.  of  the  barium  hy- 
droxide. Representing  this  difference  by  n,  the  amount  of  carbon 


382  GAS  ANALYSIS 

dioxide  in  the  sample  may  be  calculated  by  means  of  the  fol- 
lowing proportion: 

— :  volume  of  air  sample  taken  =  x  :  10,000 

in  which  x  represents  the  parts  of  carbon  dioxide  per  10,000  of  air. 

The  Pettersson-Palmqvist  Method.  —  Of  the  second  type 
of  methods  for  the  determination  of  small  percentages  of  car- 
bon dioxide,  that  devised  by  Pettersson  and  Palmqvist 1  is  one 
of  the  most  satisfactory  and  accurate. 

The  apparatus  that  they  designed  permits  of  the  measure- 
ment of  as  small  a  volume  of  air  as  25  cc.  with  an  accuracy  of 
one  part  in  10,000,  and  avoids  the  necessity  of  making  cor- 
rections for  variations  in  pressure  and  temperature.  This  is 
made  possible  by  the  use  of  a  compensating  tube  that  is  filled 
with  air  and  that  stands  in  communication  with  one  side  of  a 
manometer  tube,  the  burette  in  which  the  air  is  measured  being 
attached  to  the  other  side  of  the  manometer.  Both  compensat- 
ing tube  and  burette,  which  are  of  nearly  the  same  capacity, 
stand  in  a  vessel  of  water.  If  the  temperature  of  this  sur- 
rounding water  changes  during  the  experiment  the  effect  upon 
the  volume  of  air  in  each  tube  is  the  same. 

If,  now,  the  two  tubes  are  always  brought  into  communication 
with  the  manometer  when  the  air  in  the  burette  is  measured,  it 
follows  that  if  the  liquid  in  the  manometer  is  brought  to  the 
same  point  in  each  case,  the  air  in  the  burette  is  measured  under 
exactly  the  same  conditions  of  pressure  and  temperature  as  pre- 
vail in  the  compensating  tube,  and  since  the  inclosed  volume 
of  air  in  the  compensating  tube,  which  is  of  course  unaffected  by 
changes  in  barometric  pressure,  is  at  each  measurement  brought 
back  to  the  volume  corresponding  to  the  original  conditions  of 
temperature  and  pressure,  the  air  in  the  burette  is  similarly 
affected,  and  for  this  reason  no  corrections  for  changes  in  tem- 
perature and  pressure  are  necessary. 

The   apparatus   of   Pettersson   and   Palmqvist,   with   slight 

1  Berichte  der  deutschen  chemischen  Gesellschaft,  20  (1887),  2129. 


EXAMINATION  OF  ATMOSPHERIC  AIR  383 

modifications  introduced  by  the  author,  is  shown  in  Fig.  106. 
The  air  is  measured  in  the  burette  A  which  contains  25  cc.  from 
a  mark  on  its  upper  capillary  tube  down  to  the  zero  point  at 
the  lower  end  of  the  capillary  S.  This  capillary  is  calibrated 
in  divisions  each  of  which  amounts  to  i0,ooo  part  of  the  total 
volume  of  the  burette.  The  somewhat  wider  capillary  T  is 
calibrated  in  divisions  that  represent  1>0100  part  of  the  vol- 
ume of  the  burette.  The  lower  end  of  T  is  connected  by  means 
of  a  piece  of  rubber  tubing  with  the  glass  stopcock  V;  this  rubber 
tube  can  be  compressed  by  turning  the  screw  N  and  forcing  down 
upon  the  tube  a  flat  metal  plate  attached  to  the  end  of  the  screw. 
The  lower  tube  of  the  stopcock  V  is  joined  to  the  level-bulb  E 
by  a  piece  of  enamelled  rubber  tubing.  At  the  upper  end  of  the 
burette  A  are  three  branch  capillary  tubes.  The  one  to  the  left 
in  the  drawing  is  provided  with  the  two-way  stopcock  /  through 
which  the  sample  of  air  is  drawn  into  the  apparatus  either  di- 
rectly from  the  outer  atmosphere  through  P  or  through  the  coil 
of  copper  tubing  H  and  the  glass  tube  /.  At  the  right,  A  is  con- 
nected through  the  stopcock  L  with  an  Orsat  gas  pipette  B 
that  contains  glass  tubes  and  is  charged  with  a  solution  of  potas- 
sium hydroxide  for  the  absorption  of  carbon  dioxide.  The  other 
branch  capillary  tube  joins  A  through  the  stopcock  K  to  the 
manometer  M  which  may  be  brought  into  communication  with 
the  outer  air  by  opening  the  stopcocks  F  and  G.  The  other 
end  of  M  is  connected  by  the  rubber  tube  D  to  the  glass  com- 
pensating tube  C.  The  burette  A,  the  pipette  B,  the  compensat- 
ing tube  C  and  the  coil  of  copper  tube  H  as  well  as  the  capillary 
tubes  S  and  T  are  surrounded  by  water  that  is  contained  in  the 
wide  glass  cylinder  and  in  the  jacket  tube  around  the  lower 
capillaries.  The  whole  apparatus  is  mounted  on  a  board  about 
90  cm.  high  and  30  cm.  wide  which  is  itself  set  into  a  square 
wooden  base.  The  apparatus  can  be  covered  by  a  wooden  box 
that  slides  down  over  it  and  that  is  held  in  place  by  the  screws 
shown  at  the  top  of  the  board.  This  cover  does  not  appear  in 
the  figure. 


GAS  ANALYSIS 


FIG.  106 


EXAMINATION  OF  ATMOSPHERIC  AIR  385 

The  manometer  M  contains  a  drop  of  petroleum  in  which 
azobenzene  is  dissolved  and  there  is  etched  upon  the  surface  of 
the  tube  a  scale  by  means  of  which  the  position  of  the  drop 
may  be  read. 

The  coil  of  copper  tube  H  has  been  added  to  the  original 
Pettersson-Palmqvist  apparatus  because  it  has  been  found,  in 
determining  the  carbon  dioxide  in  the  air  of  rooms  that  are  or 
recently  have  been  occupied,  that  it  takes  several  minutes  for 
the  sample  of  warm  air  from  the  upper  part  of  the  room  to  fall 
to  the  temperature  of  the  water  that  surrounds  A.  This  is 
shown  by  the  side  movement  of  the  drop  of  liquid  in  the  manom- 
eter after  the  sample  has  been  measured.  If,  however,  instead 
of  drawing  the  air  directly  into  A  through  P  it  is  caused  to  pass 
through  the  coil  H,  which  is  about  80  cm.  long,  3  mm.  internal 
diameter,  and  5  mm.  external  diameter,  the  entering  sample  of 
air  is  rapidly  cooled  (or  warmed)  to  the  temperature  of  the  sur- 
rounding water. 

It  has  oftentimes  been  noticed  that  the  change  in  the  volume 
of  the  sample  of  air  in  A  that  is  caused  by  its  rising  or  falling 
to  the  temperature  of  the  surrounding  water,  produces  a  greater 
movement  of  the  manometer  liquid  than  would  result  from  the 
removal  of  the  carbon  dioxide  in  the  sample. 

In  making  a  determination  of  carbon  dioxide  with  this  ap- 
paratus, clean  mercury  is  poured  into  the  level-bulb  E  in  an 
amount  sufficient  to  fill  the  connecting  tubes  and  the  burette  A . 
The  stopcock  J  is  turned  to  such  position  that  A  communicates 
with  P,  and  one  drop  of  water  is  introduced  into  the  end  of  the 
tube  and  is  drawn  over  into  A.  The  absorption  tube  B  is  then 
filled  with  a  33  per  cent  solution  of  potassium  hydroxide.  The 
apparatus  is  now  transferred  to  the  place  where  the  air  or  other 
gas  mixture  is  to  be  examined.  The  glass  cylinder  surrounding 
the  absorption  and  measuring  tubes  is  filled  with  water  of  the 
temperature  of  the  surrounding  air.  Stopcocks  V  and  /  are 
now  opened,  the  level-bulb  E  is  raised,  and  mercury  is  driven 
nearly  to  the  top  of  the  burette  A.  /is  now  closed,  the  level- 


386  GAS  ANALYSIS 

bulb  E  is  lowered,  the  stopcock  L  is  carefully  opened,  and  the 
solution  of  potassium  hydroxide  in  the  absorption  tube  B  is 
drawn  up  to  a  mark  on  the  stem  at  which  this  solution  must 
always  stand  when  measurements  are  made.  L  is  then  closed, 
J  is  turned  to  such  position  that  A  communicates  with  P  and 
the  mercury  in  the  burette  A  is  raised  until  it  stands  at  the  mark 
on  the  capillary  tube  above  the  burette.  The  level-bulb  E  is 
now  slowly  lowered,  and  air  is  drawn  into  A  until  the  mercury 
falls  to  about  the  point  T.  J  is  then  turned  to  such  position 
that  A  communicates  with  the  coil  H  and  the  level-bulb  is  now 
raised  and  this  first  sample  of  air  is  driven  out  through  the 
outlet  7.  A  second  sample  is  now  drawn  in  through  /  and  H 
by  lowering  E,  the  mercury  being  allowed  to  fall  to  a  point 
slightly  below  the  zero  mark  on  the  capillary  tube  S.  The  stop- 
cocks /  and  V  are  then  closed  and  the  rubber  tube  at  the  bottom 
of  the  measuring  burette  is  compressed  by  turning  the  screw 
N  until  the  mercury  stands  exactly  at  the  zero  mark  of  the 
tube  S.  The  stopcock  /  is  then  opened  for  a  moment  to  bring 
the  sample  in  the  burette  A  to  atmospheric  pressure.  The  stop- 
cocks F  and  G  are  next  carefully  opened  to  bring  the  air  upon 
both  sides  of  the  manometer  and  in  the  compensating  tube  C  to 
atmospheric  pressure.  In  this  operation  care  must  be  exercised 
to  avoid  driving  out  the  drop  of  liquid  from  the  tube  M .  F  and 
G  are  now  closed,  the  stopcock  K  is  carefully  opened,  and  the 
position  of  the  drop  of  liquid  in  the  manometer  M  is  noted. 
The  stopcock  K  is  then  closed,  the  stopcocks  V  and  then  L  are 
opened,  and  the  sample  of  air  is  driven  over  into  the  absorption 
pipette  B  where  it  is  allowed  to  remain  for  one  minute  in  contact 
with  the  absorbent.  The  level-bulb  E  is  then  lowered  and  the 
solution  of  potassium  hydroxide  in  B  is  drawn  up  again  to  the 
mark,  whereupon  L  is  closed.  The  residual  gas  in  the  burette  A 
is  now  brought  approximately  to  atmospheric  pressure  by  proper 
adjustment  of  the  height  of  the  level-bulb  E  and  the  stopcock  V 
is  then  closed.  K  is  opened  and  the  drop  of  liquid  in  the  manom- 
eter M  is  brought  to  its  original  position  by  turning  the  com- 


EXAMINATION  OF  ATMOSPHERIC   AIR  387 

pression  screw  N.  The  final  volume  of  the  gas  is  now  read  off 
on  the  capillary  tube  S  and  the  difference  between  this  reading 
and  the  reading  of  the  initial  volume,  expressed  in  divisions  on 
this  tube,  corresponds  to  the  parts  of  carbon  dioxide  per  10,000 
in  the  sample  of  air  under  examination. 

If  the  carbon  dioxide  in  the  sample  is  higher  than  0.4  per  cent, 
the  wider  calibrated  capillary  tube  T  is  employed  in  making 
the  measurements,  one  division  on  this  tube  corresponding  to 
one  part  of  carbon  dioxide  per  1,000  parts  of  air. 

A  serious  objection  to  the  Pettersson-Palmqvist  apparatus 
is  its  size  and  weight.  It  is  also  quite  difficult  to  replace  any  of 
the  glass  parts  that  may  be  broken.  Modifications  of  the  ap- 
paratus, with  a  view  to  making  it  more  easily  portable,  have 
been  proposed  by  Bleier  l  and  Rogers,  but  in  the  opinion  of  the 
author,  the  objections  to  the  original  form  are  most  satisfac- 
torily met  by  the  device  described  by  Anderson  2  and  shown  in 
Fig.  107. 

Anderson's  Modification  of  the  Pettersson-Palmqvist 
Apparatus.  —  The  gas  is  measured  in  the  burette  A  and  the 
change  in  volume  of  the  sample  that  results  when  the  carbon 
dioxide  is  absorbed  is  read  upon  the  capillary  S.  This  bent 
capillary  tube  passes  through  a  stopper  and  is  joined  to  the 
stopcock  V  by  a  piece  of  rubber  tubing.  This  rubber  tube 
passes  under  the  compression  screw  N  by  means  of  which  the 
fine  adjustment  of  the  mercury  in  the  capillary  tube  51  is  effected. 
The  other  side  of  the  stopcock  V  is  connected  with  the  level- 
bulb  E  by  a  piece  of  enamelled  'rubber  tubing.  A  solution  of 
potassium  hydroxide  for  the  absorption  of  carbon  dioxide  is 
contained  in  the  pipette  B,  C  is  the  compensating  tube,  and  M 
the  manometer.  By  means  of  the  three-way  stopcock  /  the 
sample  of  air  may  be  drawn  through  the  coil  of  copper  tubing 
H,  H',  H".  The  compensating  tube  C  may,  by  means  of  the 
three-way  stopcock  F,  be  brought  into  communication  with  the 

1  Z.f.  Hygiene,  27  (1898),  in. 

2J.  Amer.  Chem.  Soc.  35  (1913),  162. 


388 


GAS  ANALYSIS 


FIG.  107 


EXAMINATION  OF  ATMOSPHERIC  AIR          389 

atmosphere  through  the  side  arm  whenever  necessary.  The 
liquid  index  in  the  manometer  is  introduced  through  the  stop- 
cock G. 

The  burette,  pipette,  compensating  tube,  and  the  copper 
coil  are  immersed  in  water  that  is  contained  in  a  glass  cell  of 
rectangular  cross  section,  and  that  is  provided  at  the  lower  side 
with  a  neck  like  the  neck  of  a  bottle  into  which  the  rubber  stopper 
shown  in  the  figure  is  tightly  inserted.  In  addition  to  the  capillary 
tube  6*  there  passes  through  this  rubber  stopper  a  short  piece  of 
glass  tubing  through  which  the  water  in  the  cell  may  be  run 
off.  The  glass  parts  of  the  apparatus  in  the  cell  are  fastened 
to  a  sliding  board  DD  above  the  cell.  If  the  rubber  stopper 
passing  through  the  neck  of  the  cell  is  loosened,  and  the  rub- 
ber tube  is  slipped  off  from  the  lower  end  of  S,  the  appara- 
tus may  be  lifted  from  the  case  by  raising  the  board  to  which 
it  is  attached.  Ready  access  to  all  parts  of  the  apparatus 
is  thus  easily  attained,  and  the  cleaning  and  repairing  of  the 
different  portions  is  rendered  easy.  Furthermore,  the  position 
of  the  board  may  be  adjusted,  within  certain  limits,  by  means 
of  the  screw  X,  a  detail  that  is  of  importance  in  mounting  new 
glass  parts  of  slightly  different  dimensions  from  those  of  the 
older  parts.  The  case,  Fig.  108,  is  provided  with  a  removable 
front  and  top  and  with  a  pane  of  glass  at  the  the  back  to  illumi- 
nate the  apparatus  when  it  stands  between  the  operator  and 
the  window. 

This  form  of  the  Pettersson-Palmqvist  apparatus  devised 
by  Anderson  is  only  42  cm.  high  whereas  the  original  apparatus 
has  a  height  of  90  cm.  Its  small  size  and  the  ease  with  which 
it  may  be  manipulated  renders  it  distinctly  superior  to  the 
original  form. 

Before  the  apparatus  is  put  into  use  the  glass  parts  should,  if 
necessary,  be  thoroughly  cleaned,  and  the  stopcocks  should  be 
carefully  lubricated.  In  preparing  the  apparatus  for  use  about 
30  cc.  of  distilled  mercury  is  poured  into  the  level-bulb  E  and  a 
small  quantity  of  water  is  introduced  into  the  burette  through 


GAS  ANALYSIS 


FIG.  108 


EXAMINATION   OF  ATMOSPHERIC  AIR  391 

the  opening  T  directly  above  the  stopcock  /.  This  is  done  by 
covering  the  end  of  this  capillary  tube  with  a  film  of  water  and 
drawing  an  amount  of  the  liquid  sufficient  to  form  a  column  from 
3  to  5  mm.  long  in  the  capillary  tube  into  the  burette  by  lowering 
the  level-bulb. 

The  drop  of  liquid  that  is  used  in  the  manometer  (petroleum 
in  which  azobenzene  has  been  dissolved)  is  introduced  into  M  by 
filling  the  burette  A  nearly  to  the  top  with  mercury  with  the 
stopcocks  K  and  G  open,  and  then  closing  stopcock  V  and  screw- 
ing down  the  compression  screw  N.  A  small  amount  of  the 
manometer  liquid  is  now  brought  upon  the  end  of  the  capillary 
tube  upon  stopcock  G,  and  an  amount  of  the  liquid  sufficient 
to  occupy  a  length  of  from  3  to  5  mm.  in  M  is  drawn  into  the 
capillary  as  far  as  the  branch  tube  below  stopcock  G  by  turning 
back  the  compression  screw  N.  Stopcock  G  is  then  closed,  F  is 
opened  and  the  compression  screw  N  is  again  turned  down  upon 
the  rubber  tube,  and  the  liquid  is,  in  this  manner,  forced  into 
the  manometer  tube  M. 

The  pipette  B  is  filled  with  a  solution  of  potassium  hydroxide 
that  is  prepared  by  dissolving  one  part  of  potassium  hydroxide 
in  two  parts  of  water.  This  solution  is  drawn  up  to  the  mark 
on  the  capillary  by  lowering  the  level-bulb  E,  and  stopcock  L 
is  then  closed. 

Before  proceeding  with  the  determination  of  the  carbon 
dioxide  in  the  air  of  a  room,  the  apparatus  should  be  allowed  to 
stand  long  enough  in  the  room  to  insure  equilibrium  between 
the  temperature  of  the  water  in  the  water  jacket  and  the  tem- 
perature of  the  air  in  the  room.  The  air  in  the  manometer  tube 
M  and  in  the  compensating  tube  C  should  be  brought  to  atmos- 
pheric pressure  by  opening  the  stopcocks  F  and  G.  During  a 
determination  the  apparatus  should  not  stand  in  direct  sunlight 
or  in  a  draft  of  air. 

The  actual  determination  of  carbon  dioxide  is  carried  on 
as  follows :  —  Turn  stopcock  /  to  such  position  that  the  bu- 
rette A  communicates  with  the  outer  air  through  the  tube  T. 


392  GAS  ANALYSIS 

Fill  the  burette  A  with  mercury  by  opening  stopcock  V  and 
raising  the  level-bulb  E.  Turn  stopcock  /  to  such  position 
that  the  burette  A  communicates  with  the  copper  tube  H,  and 
draw  air  into  A  through  H  by  lowering  the  level-bulb  E.  Inas- 
much as  this  sample  is  mixed  with  air  that  was  already  present 
in  the  connecting  tubes  and  the  copper  tube  H,  it  is  driven  out 
through  T  by  turning  the  stopcock  /  into  the  proper  position 
and  raising  the  level-bulb.  Stopcock  /  is  then  turned  back  so 
that  A  communicates  with  H.  The  level-bulb  E  is  again  lowered 
and  the  sample  of  air  is  drawn  into  the  burette  A  until  the  mer- 
cury in  the  burette  falls  slightly  below  the  zero  mark  on  the 
capillary  tube  S.  Stopcock  V  is  then  closed  and  the  compression 
screw  N  is  turned  until  the  mercury  stands  exactly  at  the  zero 
mark.  Allow  stopcock  /  to  remain  open  for  a  few  moments  to 
allow  the  air  in  the  burette  to  assume  atmospheric  pressure  and 
then  close  /.  Open  stopcock  K  carefully,  and  read  the  position 
of  the  liquid  in  the  manometer  M.  Then  close  stopcock  K. 

To  remove  the  carbon  dioxide  in  the  sample,  open  stopcock  V 
and  then  stopcock  L  and  drive  the  gas  over  into  the  pipette  B. 
When  the  mercury  nearly  reaches  the  stopcock  L,  close  that 
stopcock  and  leave  the  gas  in  contact  with  the  potassium  hy- 
droxide for  one  minute.  Then  lower  the  level-bulb,  open  stop- 
cock L,  draw  the  gas  back  into  the  burette,  and  when  the  solution 
of  potassium  hydroxide  rises  to  the  mark  on  the  capillary  close 
stopcock  L.  Bring  the  mercury  approximately  to  the  zero 
mark  in  the  capillary  S  by  raising  or  lowering  level-bulb  E,  close 
the  stopcock  V  and  then  turn  the  compression  screw  N  until  the 
mercury  in  the  capillary  tube  S  stands  at  such  a  point  above 
the  zero  mark  as  will  correspond  approximately  to  the  percentage 
of  carbon  dioxide  in  the  air  under  examination.  Then  open 
stopcock  K  and  turn  N  until  the  liquid  in  the  manometer  stands 
at  the  position  that  is  occupied  before  the  absorption  was  made. 
The  reading  of  the  mercury  in  the  capillary  tube  S  now  gives 
directly  the  amount  of  carbon  dioxide  in  the  sample  of  air  ex- 
pressed in  parts  per  10,000. 


CHAPTER  XIX 

THE  ANALYSIS  OF  SALTPETER  AND  NITRIC  ACID  ES- 
TERS (NITROGLYCERINE,  GUN-COTTON)  WITH  THE 
NITROMETER 

Walter  Crum  1  observed  that  the  higher  oxides  of  nitrogen 
are  completely  reduced  to  nitric  oxide  when  absorbed  in  sul- 
phuric acid  and  then  shaken  with  mercury.  John  Watts 2 
and  Georg  Lunge  3  developed  this  method  still  further,  and 
the  latter  constructed  an  apparatus  therefor  which  he  termed 
a  nitrometer.  Hempel  utilized  4  the  reaction  in  the  decomposi- 
tion of  the  nitric  acid  esters,  and  in  particular  in  the  determina- 
tion of  the  nitroglycerine  in  dynamite.  For  this  work  he  designed 
a  special  nitrometer  which  is  also  admirably  adapted  to  the  eval- 
uation of  saltpeter.  In  its  original  form,  however,  the  Hempel 
nitrometer  is  open  to  objection  because  the  rubber  stopper  that 
carries  the  sample  tube  is  kept  in  place  only  with  difficulty,  and 
because  further  of  the  awkwardness  of  cleaning  the  apparatus 
after  a  determination  has  been  made.  The  author  has  sought  to 
remedy  these  defects  by  giving  to  the  nitrometer  the  form  shown 
in  Fig.  109. 

The  Nitrometer.  —  The  evolution  cylinder  C  is  provided  at 
the  lower  end  with  the  double-bore  stopcock  T  and  the  side 
arm  R.  The  stopcock  5,  also  of  double  bore,  is  attached  to  the 
upper  end  of  the  cylinder  by  the  carefully  ground  joint  J  and 
is  held  in  place  by  rubber  bands  slipped  over  the  small  glass 
hooks  above  and  below  the  joint.  K  is  a  capillary  tube  which 
serves  to  connect  the  nitrometer  with  the  gas  burette  in  which 

1  Philosoph.  Mag.  30  (1847),  426.  • 

2  Chemical  News,  37  (1878),  45. 

3  Berichte  der  deutschen  chemischen  Gesettschaft,  II  (1878),  434. 

4  Zeitschrijt  fur  analyt.  Chemie,  20  (1881),  82. 

393 


394 


GAS  ANALYSIS 


the  evolved  nitric  oxide  is  measured.  Lisa,  level-bulb  that  is 
joined  to  one  arm  of  the  stopcock  T  by  a  piece  of  enamelled 
rubber  tubing. 

The  manipulation  of  the  apparatus  in  the  evaluation  of 
saltpeter  or  other  nitrate  is  as  follows :  —  Place  the  evolution 

cylinder  C  in  a  large  clamp  and 
attach  it  to  an  iron  stand  in  an  up- 
right position.  Place  the  level- 
bulb  L  in  a  split  ring  that  is  also 
attached  to  the  rod  of  the  iron 
stand  and  introduce  into  L  an 
amount  of  mercury  sufficient  to 
fill  the  evolution  cylinder  C,  the 
side  arm  R,  and  the  rubber  tube 
joining  L  and  C.  Remove  the 
stopcock  S  from  the  top  of  the 
cylinder  C,  turn  the  stopcock  T 
into  such  position  that  L  and  C 
will  be  in  communication,  and  fill 
the  evolution  cylinder  C  with  mer- 
cury to  a  point  about  5  cm.  below 
the  top  of  the  tube  /.  Introduce 
into  the  upper  end  of  C  through 
the  open  tube  /  about  5  cc.  of  a 
solution  of  the  nitrate  to  be  ana- 
lyzed, running  in  the  solution  from 
the  small  burette  B,  which  is  calibrated  in  tenths  of  a  cubic 
centimeter  and  can  easily  be  read  to  fiftieths.  Place  the  stop- 
cock S  upon  /  and  fasten  it  in  position  by  rubber  bands  at- 
tached to  the  small  hooks  on  either  side  of  the  joint.  Raise 
the  level-bulb  until  the  top  of  the  solution  in  C  just  reaches 
the  lower  side  of  the  stopcock  S  and  then  close  61  and  T. 
Lower  the  level-bulb  L  and  then  carefully  open  the  stopcock 
T  until  the  mercury  in  the  side  arm  R  falls  to  about  the  begin- 
ning of  the  bend  in  that  tube. 


ANALYSIS  OF  SALTPETER  AND  NITRIC  ACID    395 

Introduce  a  measured  amount  (about  20  cc.)  of  concentrated 
sulphuric  acid  into  the  upper  open  end  of  R.  Remove  C  from 
the  clamp  and  hold  it  in  an  inclined  position,  with  the  tube  R 
on  the  upper  side,  at  such  height  that  the  mercury  in  R  stands 
at  the  same  level  as  that  in  the  level-bulb  L.  Turn  the  stop- 
cock T  to  such  position  that  L  communicates  with  C  and  then 
slowly  raise  C  (still  holding  it  in  an  inclined  position)  until 
all  but  about  5  cc.  of  the  sulphuric  acid  has  been  drawn  into 
the  evolution  cylinder  C.  Now  lower  C  until  the  mercury  rises 
to  about  the  middle  of  the  tube  R  and  then  close  the  stopcock  T. 
Shake  the  cylinder  C  to  insure  intimate  mixing  of  the  sulphuric 
acid  with  the  solution  of  the  nitrate.  As  the  reaction  proceeds 
the  evolution  of  gas  tends  to  force  the  mercury  upwards  in  the 
side  arm  R.  The  level  of  the  mercury  in  this  arm  is  kept  ap- 
proximately the  same  during  the  reaction  by  opening  the  stop- 
cock T  from  time  to  time  and  allowing  the  mercury  to  flow  back 
into  the  level-bulb  L.  The  shaking  of  the  evolution  cylinder  C 
is  continued  until,  with  the  stopcock  T  closed,  no  further  rise 
of  the  mercury  in  R  is  observed.  The  reaction  is  then  complete. 

C  is  now  again  clamped  in  a  vertical  position  and  the  capillary 
tube  K  is  attached  by  means  of  a  small  L-shaped  piece  of  capil- 
lary tubing  to  a  Hempel  gas  burette  that  contains  mercury  as 
the  confining  liquid  and  into  which  a  very  little  water  has  been 
introduced.  The  stopcock  S  is  then  turned  to  such  position  as 
to  connect  K  with  the  outlet  M ,  and  the  level -tube  of  the  burette 
is  raised  until  the  capillary  tube  K  is  completely  filled  with 
mercury.  S  is  now  turned  through  180°  so  that  the  cylinder  C 
communicates  with  the  tube  K.  T  is  then  turned  to  such  posi- 
tion that  L  and  C  are  connected,  and  the  evolved  gas  is  drawn 
over  into  the  burette,  the  sulphuric  acid  in  the  nitrometer  being 
allowed  to  follow  the  gas  until  it  almost  reaches  the  end  of  the 
capillary  tube  K.  The  stopcock  S  is  then  closed,  the  pinchcock 
at  the  top  of  the  burette  is  also  closed  and  the  nitric  oxide  in  the 
burette  is  measured  in  the  usual  manner,  due  allowance  being 
made  for  the  tension  of  water  vapor. 


396  GAS  ANALYSIS 

After  a  determination  has  been  made,  the  nitrometer  is 
cleaned  by  lowering  the  level-bulb,  opening  the  stopcocks  ,S 
and  T  and  allowing  the  clean  mercury  to  flow  back  into  the 
bulb  L.  The  stopcock  T  is  then  turned  into  the  position  shown 
in  the  figure  and  the  dirty  mercury,  mercurous  sulphate,  and 
sulphuric  acid  are  allowed  to  run  out  through  the  tube  N  into  a 
beaker.  The  stopcock  6*  is  next  slipped  off  from  the  upper  end  of 
the  cylinder  C  and  the  side  arm  R  as  well  as  the  wide  tube  of  the 
stopcock  5*  are  thoroughly  rinsed  with  water  and  are  then  dried. 

In  calculating  the  results  of  the  analysis  allowance  must  be 
made  for  the  solubility  of  nitric  oxide  in  sulphuric  acid.  15  cc. 
of  sulphuric  acid  will  dissolve  about  0.2  cc.  of  nitric  oxide. 

The  purity  of  the  nitric  oxide  that  is  evolved  may  be  ascer- 
tained by  passing  the  gas,  after  it  has  been  measured  in  the 
burette,  into  a  double  gas  pipette  for  liquid  reagents  that  con- 
tains in  the  first  two  bulbs  a  solution  of  a  ferrous  salt,  and  in  the 
last  two,  water.  The  analytical  absorbing  power  of  a  saturated 
solution  of  ferrous  chloride  is  14,  and  of  ferrous  sulphate  about  4. 

In  the  evaluation  of  saltpeter  the  sample  should  be  dissolved 
in  a  little  water  and  5  cc.  of  this  solution  is  used  in  the  analysis. 
The  concentration  of  this  solution  should  be  such  that  about 
75  cc.  of  nitric  oxide  will  be  evolved. 

In  the  analysis  of  solid  material  a  weighed  sample  of  the 
substance  is  introduced  into  the  upper  open  end  of  the  evolution 
cylinder  C.  The  sample  is  moistened  with  a  little  water,  the 
stopcock  6*  is  then  placed  in  position  and  fastened  with  rubber 
bands,  mercury  is  driven  up  to  the  lower  side  of  the  stopcock  S, 
and  the  further  analysis  is  then  carried  out  in  the  manner  above 
described. 

In  the  analysis  of  gun-cotton  Hagen  first  shakes  the  sample 
with  concentrated  sulphuric  acid  in  the  evolution  cylinder  C  for 
three  minutes,  and  then  when  the  gun-cotton  is  dissolved,  he 
heats  C  by  holding  it  in  an  inclined  position  over  a  Bunsen 
burner,  and  continues  the  shaking  of  C  as  long  as  evolution 
of  gas  is  observed. 


CHAPTER  XX 
THE  LUNGE  NITROMETER 

The  nitrometer  of  Lunge  1  was  originally  designed  for  the 
evaluation  of  nitrates.  For  this  specific  purpose  it  is  inferior  to 
the  nitrometer  described  in  Chapter  XIX,  because  the  nitric 
oxide  is  evolved  in  the  tube  in  which  the  gas  volume  is  finally 
read,  and  the  foaming  of  the  acid  renders  difficult  the  accurate 
reading  of  the  height  of  the  confining  liquid. 

A  modified  form  of  his  nitrometer  which  Lunge  later  described2 
under  the  name  of  a  ureometer,  but  which  is  generally  known 
under  the  name  of  the  Lunge  nitrometer,  is  an  instrument  of 
wide  application  in  gas-volumetric  analysis.3 

The  Lunge  Nitrometer.  —  The  instrument  (Fig.  no)  con- 
sists of  a  gas  burette  A,  a  level- tube  B,  and  an  evolution  flask  C. 
The  burette  has  a  capacity  of  more  than  100  cc.  It  is  provided 
at  the  upper  end  with  a  two-bore  stopcock,  and  is  graduated 
from  the  stopcock  downward  in  -J-  cc. 

One  of  the  two  tubes  of  the  stopcock  is  a  short  upright 
capillary  tube  of  the  usual  diameter:  the-  other  tube  is  some- 
what larger  and  is  bent  over  until  it  points  nearly  downward. 
To  it  the  evolution  flask  C  is  joined  by  a  short  piece  of  rubber 
tubing,  the  ends  of  the  glass  tubes  being  brought  nearly  together. 

The  evolution  flask  C  usually  has  a  capacity  of  about  100  cc. 
A  short  tube,  open  at  the  top,  is  fused  to  the  bottom  of  the  flask. 
A  soft,  one-hole  rubber  stopper  carrying  a  short  glass  tube 
is  inserted  in  the  neck  of  C. 

1  Berichte  der  deutschen  chemischen  Gesellschqft,  1 1  (1878),  434;  ibid,  21  (1888),  376. 

2  Berichte  der  deutschen  chemischen  Gesellschaft,  18  (1885),  2030. 

3  See  A.  H.  Allen,  /.  Soc.  Chem.  Ind.  4  (1885),  178;  Lunge,  Chemische  Industrie, 
1885,  i6i;J.Ss£.  Chem. Ind.,  g  (1890),  21. 

397 


398 


GAS   ANALYSIS 


Manipulation  of  the  Lunge  Nitrometer.  —  In  making  a  de- 
termination with  the  nitrometer,  water  or  mercury  is  poured 
into  the  open  end  of  the  level-tube  B,  the  stopcock  D  is 

opened,  and  the  confining 
liquid  is  allowed  to  rise  nearly 
to  the  stopcock  which  is  then 
closed.  The  reacting  sub- 
stances are  now  placed  in  the 
evolution  flask  C,  one  in  the 
outer  space,  the  other  in  the 
tube.  The  short  rubber  tube 
carrying  the  stopper  of  C  is 
slipped  over  the  end  of  the 
bent  tube  of  D,  and  the  rub- 
ber stopper  is  then  tightly 
inserted  into  the  neck  of  the 
evolution  flask.  In  doing 
this  the  neck  of  the  evolution 
flask  should  be  grasped  be- 
tween the  thumb  and  fingers 
of  one  hand  and  the  stopper 
be  pushed  into  the  neck  of 
the  flask  with  the  other  hand. 
The  body  of  the  flask  itself 
should  not  be  touched  by  the 
hand  during  the  operation 
because  this  would  warm  the 
air  in  the  flask  and  would 
cause  error  in  the  next  ad- 
justment. The  air  in  C  is 
slightly  compressed  by  the 
insertion  of  the  stopper.  It 
is  brought  to  atmospheric 
pressure  by  turning  the  stop- 


FIG.  no 


cock  D  so  that  the  evolution 


THE  LUNGE  NITROMETER  399 

flask  connects  with  the  burette,  and  then  bringing  the  confining 
liquid  in  the  level-tube  to  the  same  height  as  that  in  the  burette. 
The  air  in  the  evolution  flask  is  now  at  atmospheric  pressure. 
The  stopcock  D  is  turned  through  180°  while  the  tubes  are  in 
this  position,  and  the  level-tube  is  then  raised  until  all  of  the 
air  in  the  burette  is  driven  out  through  the  open  capillary  tube 
of  the  stopcock.  The  stopcock  is  turned  to  join  A  to  C,  and 
the  substances  in  the  evolution  flask  C  are  then  brought  to- 
gether by  taking  hold  of  the  rubber  stopper  of  the  flask  and  tip- 
ping it.  The  flask  itself  should  not  be  touched  with  the  hand. 
The  reaction  is  allowed  to  proceed  to  completion,  the  flask  being 
occasionally  gently  shaken.  The  gas  that  is  set  free  passes 
over  into  the  burette.  The  pressure  thus  caused  is  relieved  from 
time  to  time  by  lowering  the  level-tube.  When  the  evolution 
of  gas  has  ceased,  the  confining  liquid  in  the  burette  and  level- 
tube  is  brought  to  the  same  height,  and  the  volume  of  gas  in  the 
burette  is  read  off.1  The  thermometer  and  barometer  are  read 
and  the  gas  volume  is  corrected  to  standard  conditions.  The 
necessity  for  this  correction  may  be  avoided  by  using  the  Lunge 
gas  volumeter  (see  p.  37)  in  place  of  the  nitrometer. 

As  illustrative  of  the  many  and  various  gas  volumetric  de- 
terminations that  may  be  made  with  the  Lunge  nitrometer 
(or  with  the  Lunge  gas  volumeter)  the  standardization  of  po- 
tassium permanganate,  the  determination,  of  the  active  oxygen 
in  hydrogen  dioxide,  the  determination  of  the  available  chlorine 
in  " chloride  of  lime,"  the  evaluation  of  pyrolusite,  and  the  de- 
termination of  carbon  dioxide  in  sodium  carbonate  will  here  be 
described. 

The  nitrometer  should  be  thoroughly  rinsed  with  distilled 
water  before  a  determination  is  begun,  and  the  evolution  flask 
should  be  carefully  cleaned  and  dried.  The  apparatus  should 

1  If  the  heat  of  reaction  of  the  substances  in  the  evolution  flask  is  appreciable,  a 
beaker  containing  water  of  the  temperature  of  the  room  should  be  brought  up  under 
the  flask  after  the  reaction  is  complete  and  the  flask  should  be  allowed  to  stand  im- 
mersed in  the  water  for  a  period  of  five  minutes  before  the  volume  of  gas  in  the 
burette  is  measured. 


400  GAS  ANALYSIS 

stand  in  a  room  of  even  temperature  and  should  be  protected 
from  direct  sunlight  and  drafts  of  air.  The  manipulation  gen- 
eral to  all  of  the  various  determinations  has  already  been  de- 
scribed above. 

The  Standardization  of  Potassium  Permanganate.  —  A 
solution  of  potassium  permanganate  that  is  acidulated  with 
sulphuric  acid  reacts  upon  hydrogen  dioxide  in  accordance  with 
the  equation  — 

2  KMnO4  +  3  H2SO4  +  5  H202  = 
K2SO4  +  2  MnSO4  +  8  H2O  +  5  02. 

From  this  it  appears  that 

80  parts  by  weight  of  oxygen  is  equivalent  to  158.03  parts 
by  weight  of  KMnO4. 

Since  one  cc.  of  oxygen,  under  standard  conditions,  weighs 
0.00143  §ramj  each  cubic  centimeter  of  evolved  oxygen,  reduced 
to  standard  conditions,  is  equivalent  to  0.0028247  gram  of 
KMnO4. 

If  the  solution  of  potassium  permanganate  is  approximately 
decinormal  in  strength,  25  cc.  of  the  solution  is  placed  in  the 
outer  compartment  of  the  evolution  flask,  and  5  cc.  of  normal 
sulphuric  acid  is  added  to  it.  About  5  cc.  of  a  3%  solution 
of  hydrogen  dioxide  is  then  placed  in  the  inner  tube  of  the 
flask. 

The  apparatus  is  now  connected  up,  the  air  in  the  evolution 
flask  is  brought  to  atmospheric  pressure,  the  stopcock  of  the 
burette  is  turned  so  that  the  flask  communicates  with  the  bu- 
rette, and  the  evolution  flask  is  then  tipped  and  the  hydrogen 
dioxide  is  slowly  run  out  into  the  solution  of  potassium  perman- 
ganate, the  evolution  bottle  being  constantly  shaken.  The 
level-tube  is  lowered  from  time  to  time  to  keep  the  gas  in  the 
burette  at  approximately  atmospheric  pressure.  After  the  evolu- 
tion of  the  oxygen  has  ceased,  the  gas  is  measured  and  is  re- 
duced to  standard  conditions.  The  solution  in  the  evolution 
flask  should  be  colorless  after  the  reaction  has  taken  place.  If 


THE  LUNGE  NITROMETER  401 

it  should  still  show  the  color  of  potassium  permanganate,  too 
little  hydrogen  dioxide  has  been  used.  If  25  cc.  of  the  solution  of 
potassium  permanganate  has  been  used  in  the  determination, 
the  grams  of  KMnCU  per  liter  of  solution  is  calculated  as  fol- 
lows: 

25  :  100  =  cc.  O2  X  0.0028247:  grams  KMnO4  per  liter. 

The  Determination  of  Active  Oxygen  in  Hydrogen 
Dioxide. —  The  reaction  between  acidulated  potassium  per- 
manganate and  hydrogen  dioxide  that  has  just  been  discussed 
is  utilized  in  this  determination  also. 

A  saturated  solution  of  potassium  permanganate  is  employed, 
and  an  amount  of  this  solution  (usually  about  10  cc.)  more  than 
sufficient  to  convert  all  of  the  sample  of  hydrogen  dioxide  into 
water  and  oxygen  is  placed  in  the  inner  tube  of  the  evolution 
flask. 

If  commercial  hydrogen  dioxide  of  the  usual  strength  (about 
3  per  cent)  is  under  examination,  it  must  first  be  diluted.  10  cc. 
of  the  solution  is  run  into  a  100  cc.  measuring  flask  from  a  pipette 
or  burette,  and  the  flask  is  then  filled  to  the  mark  and  is  shaken. 
10  cc.  of  this  diluted  solution  of  hydrogen  dioxide  and  20  cc.  of 
dilute  (normal)  sulphuric  acid  are  placed  in  the  outer  space  of 
the  evolution  flask.  The  reaction  is  now  effected  in  the  usual 
manner.  The  solution  in  the  evolution  ilask  must  show  the 
color  of  potassium  permanganate  after  the  evolution  of  oxygen 
has  ceased.  If  the  liquid  is  colorless,  it  indicates  that  too  little 
potassium  permanganate  has  been  used,  and  that  the  hydro- 
gen dioxide  has  not  been  completely  decomposed. 

The  results  are  calculated  in  the  manner  described  under  the 
preceding  determination,  due  allowance  being  made  for  the 
dilution  of  the  hydrogen  dioxide. 

The  Determination  of  the  Available  Chlorine  in  "  Chloride 
of  Lime."  —  Chloride  of  lime  acts  upon  hydrogen  dioxide  as 
follows: 

CaOCl2  +  H202  =  CaCl2  +  H2O  +  O2 


402  GAS  ANALYSIS 

Each  molecule  of  oxygen  evolved  is  equivalent  to  a  molecule 
of  available  chlorine  in  the  bleaching  powder,  or 

i  cc.  O2    =  i  cc.  C12  =  0.003166  gram  chlorine. 

The  calculation  of  the  result  of  the  analysis  is  simplified  if  a 
sample  of  bleaching  powder  of  exactly  0.3166  gram  is  used, 
for  then 

i  cc.  oxygen  =  i  per  cent  available  chlorine. 

7.917  grams  of  the  sample  of  chloride  of  lime  is  placed  in  a 
250  cc.  measuring  flask  which  is  then  filled  up  to  the  mark  and 
thoroughly  shaken.  10  cc.  of  the  resulting  turbid  bleach  solu- 
tion, which  will  contain  0.3166  gram  of  the  chloride  of  lime,  is 
drawn  up  into  a  pipette  and  is  run  into  the  outer  compartment 
of  the  evolution  flask.  The  measuring  flask  should  be  vigor- 
ously shaken  just  before  the  sample  is  drawn  off  into  the 
pipette. 

About  six  cc.  of  a  solution  of  hydrogen  dioxicle  containing 
approximately  1.5  per  cent  H2O2  is  introduced  into  the  inner 
tube  of  the  flask,  and  the  determination  is  then  carried  out  in 
the  usual  manner. 

The  evolved  oxygen  is  reduced  to  standard  conditions.  Each 
cubic  centimeter  of  the  gas  is  equivalent  to  one  per  cent  of  avail- 
able chlorine  in  the  chloride  of  lime. 

The  Evaluation  of  Pyrolusite.  —  Manganese  dioxide  reacts 
with  hydrogen  dioxide  in  the  presence  of  sulphuric  acid  in  ac- 
cordance with  the  equation  — 

MnO2  +  H2O2  +  H2SO4  =  MnSO4  +  2  H2O  +  O2. 
i  cc.  evolved  oxygen  =  0.003885  gram  MnO2. 

If  0.3885  gram  of  pyrolusite  is  used  in  the  determination, 
each  cubic  centimeter  of  evolved  oxygen,  reduced  to  standard 
conditions,  is  equivalent  to  one  per  cent  of  MnO2  in  the  ore. 


THE  LUNGE  NITROMETER  403 

The  weighed  sample  of  very  finely  powdered  manganese  ore 
is  placed  in  the  outer  compartment  of  the  evolution  flask.  5  cc. 
of  a  normal  solution  of  sulphuric  acid  is  run  in  upon  the  pyrolu- 
site.  25  cc.  of  a  three  per  cent  solution  of  hydrogen  dioxide 
is  next  introduced  into  the  inner  tube  of  the  flask.  The  flask 
is  allowed  to  stand  unstoppered  for  about  five  minutes  or  un- 
til the  sulphuric  acid  has  decomposed  any  carbonates  that 
may  be  present  in  the  pyrolusite.  When  the  evolution  of  gas 
from  the  material  in  the  outer  compartment  of  the  evolution 
flask  has  entirely  ceased,  the  flask  is  connected  to  the  gas  burette 
in  the  usual  manner  and  the  hydrogen  dioxide  is  brought  into 
contact  with  the  pyrolusite.  The  evolution  flask  is  shaken  for 
two  minutes  at  the  end  of  which  time  the  reaction  should  be 
complete.  If  black  particles  of  pyrolusite  are  still  to  be  seen 
in  the  flask,  the  determination  should  be  discarded  and  the  ore 
should  be  more  finely  ground  before  a  fresh  sample  is  weighed 
out.  The  evolution  flask  should  be  shaken  from  time  to  time. 
If  0.3885  gram  of  pyrolusite  has  been  used,  the  number  of  cubic 
centimeters  of  evolved  oxygen,  reduced  to  standard  conditions, 
represents  the  per  cent  of  maganese  dioxide  in  the  ore. 

The  Determination  of  Carbon  Dioxide  in  Sodium  Carbon- 
ate. —  In  this  determination  the  nitrometer  should  be  filled 
with  mercury  instead  of  with  water  as  the  confining  liquid  be- 
cause of  the  solubility  of  carbon  dioxide  in  water. 

About  0.15  gram  of  the  dry  sodium  carbonate  or  sodium  bicar- 
bonate under  examination  is  accurately  weighed  and  is  placed 
in  the  outer  compartment  of  the  evolution  flask.  5  cc.  of  a 
normal  solution  of  sulphuric  acid  is  placed  in  the  inner  com- 
partment, the  flask  is  connected  with  the  burette  and  is  then 
carefully  tilted  so  that  the  sulphuric  acid  slowly  drops  upon  the 
sodium  carbonate.  When  all  of  the  acid  has  been  poured  upon 
the  salt  the  evolution  flask  should  be  thoroughly  shaken.  The 
carbon  dioxide  evolved  is  measured  and  is  reduced  to  standard 
conditions.  Since  one  cubic  centimeter  of  carbon  dioxide  weighs 
0.001965  gram,  the  weight  of  the  evolved  carbon  dioxide  is  equal 


404  GAS  ANALYSIS 

to  the  corrected  volume  of  the  gas  in  cubic  centimeters  multi- 
plied by  0.001965. 

100  X  grams  CO^  evolved 


Per  cent  CO2 


weight  sodium  carbonate  in  grams. 


Some  carbon  dioxide  will  of  course  remain  dissolved  in  the 
liquid  in  the  evolution  flask.  If  very  accurate  results  are  de- 
sired it  is  preferable  to  employ  a  different  method  for  this  de- 
termination rather  than  to  attempt  to  introduce  a  correction 
for  the  amount  of  this  dissolved  gas. 


GAS  ANALYSIS 
International  Atomic  Weights,  1913 


405 


SYMBOL 

ATOMIC 
WEIGHT 

SYMBOL 

ATOMIC 
WEIGHT 

Aluminum 

Al 

27.1 

Neodymium 

Nd 

144-3 

Antimony 

.      .      Sb 

I  2O.  2 

Neon       .      .      . 

.      Ne 

2O.  2 

Argon 

.      .      A 

3Q.88 

Nickel      .      .      . 

.      Ni 

58.68 

Arsenic     . 

.     .      As 

74.96 

Niton  (radium 

Barium    . 

.      .      Ba 

137-37 

emanation) 

Nt 

222.4 

Bismuth  . 

.      .      Bi 

208.0 

Nitrogen 

.      N 

I4.OI 

Boron       .      . 

.     .      B 

II  .O 

Osmium  . 

.      Os 

190.9 

Bromine  . 

.     .      Br 

79.92 

Oxygen    .      .      . 

.      0 

16.00 

Cadmium 

Cd 

1  1  2  .  40 

Palladium     . 

.      Pd 

106.7 

Caesium  . 

.      .      Cs 

I32.8I 

Phosphorus  . 

.      P 

3I-04 

Calcium  . 

.     .      Ca 

40.07 

Platinum 

.      Pt 

195-2 

Carbon     . 

.      .      C 

12.  OO 

Potassium 

.      K 

39.10 

Cerium     . 

.     .      Ce 

140.25 

Praseodymium   . 

.      Pr 

140.6 

Chlorine  . 

.      .      Cl 

35-46 

Radium  . 

.      Ra 

226.4 

Chromium     . 

.     .      Cr 

52.0 

Rhodium 

.      Rh 

102.9 

Cobalt      .      . 

.      Co 

58.97 

Rubidium     .      . 

.      Rb 

85-45 

Columbium  . 

.     .      Cb 

93-5 

Ruthenium   .      . 

.      Ru 

101  .7 

Copper     . 

.     .      Cu 

63-57 

Samarium 

.      Sa 

150.4 

Dysprosium  . 
Erbium    .      . 

.    •    Dy 

.      .      Er 

162.5 
167.7 

Scandium 
Selenium 

.      Sc 
.      Se 

44.1 

79-2 

Europium 

.      .      Eu 

152.0 

Silicon 

.      Si 

28.3 

Fluorine  . 

.      .      F 

19.0 

Silver      „      .      . 

•      Ag 

107.88 

Gadolinium  . 

.      .      Gd 

157-3 

Sodium    .      .      . 

.      Na 

23.00 

Gallium    .      . 

.      .      Ga 

69.9 

Strontium     . 

Sr 

87-63 

Germanium  . 

.     .      Ge 

72-5 

Sulphur   . 

.      S 

32.07 

Glucinum 

.     .      Gl 

9.1 

Tantalum 

.      Ta 

181.5 

Gold  .     .     . 

Au 

107    2 

Tellurium 

.      Te 

127.5 

Helium    . 

.      .      He 

7  1    '   *" 

3-99 

Terbium 

.      Tb 

159-2 

Holmium 

.     .      Ho 

163.5 

Thallium       .      . 

Tl 

204.0 

Hydrogen 

.      .      H 

1.008 

Thorium 

.      Th 

232.4 

Indium     . 

.      .      In 

114.8 

Thulium 

.      Tm 

168.5 

Iodine 

.      .      I 

126.92 

T!n           •     •      • 

.      Sn 

119.0 

Iridium    . 

.      .      Ir 

i93-i 

Titanium 

.      Ti 

48.1 

Iron    .      .      . 

.      .      Fe 

55-84 

Tungsten       .      . 

.      W 

184.0 

Krypton  .      . 

.      .      Kr 

82.92 

Uranium 

.      U 

238-5 

Lanthanum   . 

.      .      La 

139.0 

Vanadium 

.      V 

51-0 

Lead  . 

Pb 

207.  10 

Xenon 

.      Xe 

130.2 

Lithium   . 

.      .      Li 

6-94 

Ytterbium 

Lutecium 

.     .      Lu 

174.0 

(Neoytterbium) 

Yb 

172.0 

Magnesium   . 

.     .      Mg 

24.32 

Yttrium  .      .      . 

.      Yt 

89.0 

M^anganese 

Mn 

^4.   0"^ 

Zinc         .     ..    .  - 

Zn 

65  .37 

Mercury  . 

•      •      Hg 

OT*  •  Vo 

200.  6 

Zirconium 

.      Zr 

90.6 

Molybdenum 

.     .      Mo 

96.0 

4o6 


GAS  ANALYSIS 


Theoretical  Densities  of  Gases 

and  Weights  of  One  Liter  of  the  Same  at  o°  and  760  mm.  pres- 
sure, at  Sea  Level  and  Latitude  45° 


Substance 

Formula 

Molecular 
Weight 

Density 
Air  —  i 

Weight  of 
One  Liter  in 
Grams 

Acetylene      
Allylene         
Ammonia       
Arsine      

C2H2 
C3H4 
NH3 
AsH3 
Br2 

26.02 
40.03 
17.03 
77.98 
I  $Q  .  84 

0.8988 
1.3819 

0.5895 
2.696 

c;    C24Q 

1.1620 
1.7869 
0.7621 

3-485 
7   14.26 

C4Hio 

58.08 

2    0065 

2    ZQA 

Butylene        

C4H8 

56.06 

I    Q34.Q 

2    ^OIO 

Carbon  dioxide  .... 
Carbon  monoxide     .     .     ; 
Carbon  oxysulphide      .     ; 
Carbonyl  chloride    . 
Chlorine        .... 

CO2 
CO 
COS 
COC12 
C12 

44.00 
28.00 
60.07 

98.92 

7O.O2 

I.520I 
0.9673 
2.0749 
3.4168 
2    4.AQ4. 

1.9652 
i  .  2506 
2.6825 
4.4172 

3  1666 

Cyanogen      ..... 

C2N2 

Z2    O2 

I    700"? 

2    3261 

Ethane          .     .     .     ^    Y 

C2H6 

•2Q  OS 

I    0381 

I    34.21 

Ethylene 

C2H4 

28  01 

o  0684. 

I    2520 

Hydrogen                       .      . 

H2 

2    Ol6 

o  06965 

O   OOOO4. 

Hydrogen  bromide        .      . 
Hydrogen  chloride   . 
Hydrogen  fluoride    .      .      . 
Hydrogen  iodide      .      .     . 
Hydrogen  selenide   .      .      . 
Hydrogen  sulphide  .      .     . 
Hydrogen  telluride  .      .      , 
Methane        .      .      . 

HBr 
HCI 
HF 
HI 
H2Se 
H2S 
H2Te 
CH4 

80.93 
36.47 

20. 
127.93 
81.2 
34-09 
129.5 

16  03 

2.7973 

1  •  2595 
0.691 
4.4172 
2.8o6 

I-I773 
4.478 
O    ^  ^30 

3.6163 
1.6283 
0.894 
5.7106 
3.627 
1.5230 
5.789 

o  7160 

Nitric  oxide  . 
Nitrogen        ....      . 
Nitrogen  tetroxide  . 
Nitrous  oxide      .... 
Oxygen    .      .      .      . 
Phosphine     .      .      .     .   ~v 
Propane  
Propylene      .      .      .     .     .' 
Silicon  tetrafluoride       ,  '  .! 
Sulphur  dioxide 
Water  vapor       .     ..     .    ., 

NO 

N2 
NO2 
N2O 
02 
PH3 
C3H8 
C3H6 
SiF4 
S02 
H2O 

30.01 
28.02 
46.01 
44.02 
32.00 
34.06 
44.06 
42.05 
104.3 
64.07 
18.016 

1.0378 
0.9701 
1.5906 
1.5229 
i  •  1055 
1-175 
1.5204 

1-4527 
3.607 
2.2131 
0.6218 

.3417 
.2542 

.0563 
.9688 
.4292 
.520 

.966 

.8780 

4.663 

2.8611 

o  .  8040 

Atmospheric  air       .     . 

i  .0000 

1.2928 

GAS  ANALYSIS 


407 


Reduction  of  a  Gas  Volume  to  o°  and  760  mm. 

If  v  is  the  volume  of  a  gas  at  1°  and  p  mm.  pressure,  the  vol- 
ume v0  of  the  gas  at  o°  and  760  mm.  may  be  calculated  with 
the  aid  of  the  formula 

=  v P 

760  (i  +  0.00367  /). 

To  facilitate  the  reduction  of  gas  volumes  to  standard  condi- 
tions, the  values  of  the  expression  (i  +  0.003670  from  — 2°  to 
+34°  are  given  in  the  following  table: 


1 

LOE     I 

f 

i 

Log     T 

,003  7* 

6  I  +0.00367  / 

0.003  7 

i  +  0.00367  / 

O, 

0, 

I, 

9,      —  io 

—  2°.0 

99266 

00320 

°.I 

00404 

99825 

—  9 

99303 

00304 

.2 

00440 

99809 

—  .8 

99339 

00288 

3 

00477 

99793 

—  -7 

99376 

00272 

•4 

00514 

99777 

—  .6 

99413 

00256 

.5 

00551 

9976i 

—  -5 

99449 

00240 

.6 

00587 

99746 

—  4 

99486 

00224 

•7 

00624 

99730 

—  3 

99523 

00208 

.8 

00661 

99714 

—  .2 

99560 

00192 

9 

00697 

99698 

—  .1 

99596 

00176 

2.O 

00734 

99682 

—  .O 

99633 

00160 

I, 

9,      —  io 

o, 

o, 

2.1 

00771 

99666 

—O.Q 

99670 

00144 

2.2 

00807 

99651 

-0.8 

99706 

00128 

2-3 

00844 

99635 

—0.7 

99743 

001  1  2 

2.4 

00881 

996i9 

—0.6 

90780 

00096 

25 

00918 

99603 

—  o  5 

99816 

00080 

2.6 

"00954 

99588 

—0.4 

99853 

00064 

2-7 

00991 

99572 

—0.3 

99890 

00048 

2.8. 

01028 

99556 

—  0.2 

99927 

00032 

2.9 

01064 

99540 

—O.I 

99963 

00016 

30 

OIIOI 

99524 

o.o 

100000 

ooooo 

I, 

9,      —  io 

i, 

9,      —io 

3i 

01138 

99509 

+0.1 

00037 

99984 

32 

01174 

99493 

0.2 

00073 

99968 

33 

OI2II 

99477 

0-3 

OOIIO 

99952 

34 

01248 

99461 

0.4 

00147 

99936 

35 

01285 

99445 

o-5 

00184 

99920 

3-6 

OI32I 

9943° 

0.6 

OO22O 

99905 

37 

01358 

99414 

0.7 

00257 

99889 

3-8 

01395 

99398 

0.8 

OO294 

99873 

39 

OI43I 

99383 

0.9 

00330 

99857 

4-0 

01468 

99367 

I.O 

00367 

99841 

Reduction  of  a  Gas  Volume  to  o°  and  760  mm. 

Value  of  (i  +  0.00367  /)  for  /  =  4.1  to  14.0° 


t 

i  +  0.00367  1 

LOE     ' 

t 

i  +  0.00367  1 

Ln_    i  . 

g  I  +  0.00367  1 

g  i  +  0.00367  1 

i, 

9,      —10 

i, 

9,      —10 

4°.  i 

01505 

99351 

9°-  1 

03340 

98573 

4.2 

01541 

99336 

9.2 

03376 

98558 

43 

01578 

99320 

93 

03413 

98542 

44 

01615 

99304 

94 

03450 

98527 

45 

01652 

99288 

95 

03487 

98511 

4.6 

01688 

99273 

9.6 

03523 

98496 

47 

01725 

99257 

97 

03560 

98481 

4-8 

01762 

99241 

9-8 

03597 

98465 

49 

01798 

99226 

99 

03633 

98450 

50 

01835 

99210 

10.  0 

03670 

98435 

li 

9,      —10 

i, 

9,      —10 

5-i 

01872 

99195 

10.  1 

•   03707 

98420 

52 

01908 

99179 

IO.2 

03743 

98404 

53 

01945 

99163 

10.3 

03780 

98389 

54 

01982 

99148 

10.4 

03817 

98373 

55 

02019 

99132 

10.5 

03854 

98358 

56 

02055 

99117 

10.6 

03890 

98343 

5-7 

02092 

99101 

10.7 

03927 

98327 

5-8 

02129 

99085 

10.8 

03964 

98312 

59 

02165 

99070 

10.9 

04000 

98297 

6.0 

O22O2 

99054 

II.  0 

04037 

98281 

I, 

9,      —10 

i, 

9,      —  10 

6.1 

02239 

99038 

u.  i 

04074 

98266 

6.2 

02275 

99023 

II.  2 

04110 

98251 

6-3 

02312 

99007 

ii.  3 

04147 

98235 

6.4 

02349 

98992 

11.4 

04184 

98220 

6-5 

02386 

98976 

11.5 

04221 

98204 

6.6 

02422 

98961 

11.  6 

04257 

98189 

6.7 

02459 

98945 

11.7 

04294 

98174 

6.8 

02496 

98929 

n.  8 

04331 

98i59 

6-9 

02532 

98914 

11.9 

04367 

98144 

7.0 

02569 

98899 

12.  0 

04404 

98128 

I, 

9,      —  10 

i, 

9,      —10 

7i 

O26o6 

98883 

12.  1 

04441 

98113 

72 

02642 

98867 

12.2 

04477 

98098 

73 

02679 

98852 

12.3 

04514 

98083 

74 

02716 

98836 

12.4 

04551 

98067 

75 

02753 

98821 

12.5 

04588 

98052 

7-6 

02789 

98805 

12.6 

04624 

98037 

7-7 

02826 

98790 

12.7 

04661 

98022 

78 

02863 

98774 

12.8 

04698 

98006 

79 

02899 

98759 

12.9 

04734 

97991 

8.0 

02936 

98743 

13  o 

04771 

97976 

I, 

9,      —10 

i, 

9,      —  10 

8.1 

02973 

98728 

I3-I 

04808 

97961 

8.2 

03009 

98712 

13-2 

04844 

97945 

8.3 

03046 

98697 

13-3 

04881 

97930 

8.4 

03083 

98681 

13-4 

04918 

97915 

8-5 

03120 

98666 

13  5 

04955 

97900 

8.6 

03156 

98651 

13  6 

04991 

97885 

8-7 

03193 

98635 

13-7 

05028 

97869 

8.8 

03230 

98619 

13-8 

05065 

97854 

8-9 

03266 

98604 

13  9 

05101 

97839 

90 

03303 

98589 

14.0 

05138 

97824 

408 


Reduction  of  a  Gas  Volume  to  o°  and  760  mm. 

Value  of  (i  +  0.00367  /)  for  /  =14.1  to  24.0° 


/ 

i  +  0.00367  / 

Log     * 

/ 

i  +  0.00367  / 

Loe     ' 

i  +  0.00367  / 

SI  +  0.00367  1 

i, 

9,      —10 

i, 

9,      —  10 

14°.  i 

05175 

97809 

19°.  i 

07010 

97058 

14.2 

05211 

97794 

19.2 

07046 

97043 

14  3 

05248 

97779 

19  3 

07083 

97028 

14.4 

05285 

97763 

19.4 

07120 

97013 

14  5 

05322 

97748 

19  5 

07157 

96998 

14-6 

05358 

97733 

19.6 

07193 

96983 

14.7 

05395 

97718 

19.7 

07230 

96968 

14.8 

05432 

97703 

19.8 

07267 

96954 

14.9 

05468 

97688 

19.9 

07303 

96939 

15  o 

05505 

97673 

20.  o 

07340 

96924 

i, 

9,      —10 

li 

9,      —10 

15  i 

05542 

97657 

20.  i 

07377 

96909 

15  2 

05578 

97642 

20.2 

07413 

96894 

15  3 

05615 

97627 

20.3 

07450 

96879 

15-4 

05652 

97612 

20.4 

07487 

96864 

15  5 

05689 

97597 

20.5 

07524 

96850 

15-6 

05725 

97582 

20.6 

07560 

96835 

15  7 

05762 

97567 

20.7 

07597 

96820 

15-8 

05799 

97552 

20.8 

07634 

96805 

15  9 

05835 

97537 

20.9 

07670 

96791 

16.0 

05872 

97522 

21.0 

07707 

96776 

tj 

9,      —  10 

i, 

9,      —10 

16.1 

05909 

97507 

21.  1 

07744 

96761 

16.2 

05945 

97492 

21.2 

07780 

96746 

16.3 

05982 

97477 

21.3 

07817 

96731 

16.4 

06019 

97462 

21.4 

07854 

96716 

16-5 

06056 

97447 

21-5 

07891 

96702 

16.6 

06092 

97432 

21.6 

07927 

96687 

16.7 

06129 

97417 

21.7 

07964 

96672 

16.8 

06166 

97402 

21.8 

08001 

96657 

16.9 

06202 

97387 

21.9 

08037 

96643 

17.0 

06239 

97372 

22.0 

08074 

96628 

i, 

9,      —10 

i, 

9,      —10 

17.1 

06276 

97357 

22.1 

08111 

96613 

17.2 

06312 

97342 

22.2 

08147 

96598 

17  3 

06349 

97327 

22.3 

*  08184 

96584 

17.4 

06386 

97312 

22.4 

08221 

96569 

17  5 

06423 

97297 

22.5 

08258 

96554 

17-6 

06459 

97282 

22.6 

08294 

96539 

17.7 

06496 

97267 

22.7 

08331 

96525 

178 

06533 

97252 

22.8 

08368 

96510 

17.9 

06569 

97237 

22.9 

08404 

96495 

18.0 

06606 

'97222 

23.0 

08441 

96481 

i, 

9,      —10 

i, 

9,      —10 

18.1 

06643 

97207 

23-1 

08478 

96466 

18.2 

06679 

97192 

23.2 

08514 

96451 

18-3 

06716 

97177 

23  3 

08551 

96437 

18.4 

06753 

97162 

23  4 

08588 

96422 

18.5 

06790 

97147 

23  5 

08625 

96407 

18.6 

06826 

97132 

23.6 

08661 

96393 

18.7 

06863 

97117 

23  7 

08698 

96378 

18.8 

06900 

97102 

23.8 

08735 

96363 

18.9 

06936 

97088 

23  9 

08771 

96349 

19  o 

06973 

9/073 

24.0 

08808 

96334 

409 


Reduction  of  a  Gas  Volume  to  o°  and  760  mm. 

Value  of  (i  +  0.00367  i)  for  t  =24.1  to  34.0°. 


t 

i  +  0.00367  1 

Loz     x 

t 

i  +  0.00367  1 

Loc     * 

6  i  +  0.00367  t 

*  i  +  0.00367  t 

i, 

9,      —10 

i, 

9,      —io 

24°.  I 

08845 

96319 

29°.  i 

10680 

95593 

24.2 

08881 

96305 

29.2 

10716 

95579 

24  3 

08918 

96290 

29  3 

10753 

95565 

24.4 

08955 

96275 

29.4 

10790 

95550 

24  5 

08992 

96261 

29  5 

10827 

95535 

24.6 

09028 

96246 

29.6 

10863 

9552i 

24.7 

09065 

96231 

29.7 

10900 

95507 

24.8 

09102 

96217 

29.8 

10937 

95492 

24.9 

09138 

96202 

29.9 

10973 

95478 

25.0 

09175 

96188 

30.0 

IIOIO 

95464 

i, 

9,      —10 

Ii 

9,      —io 

25.1 

09212 

96173 

30.1 

11047 

95449 

25  2 

09248 

96i59 

30.2 

11083 

95435 

25  3 

09285 

96144 

30.3 

in  20 

95421 

25  4 

09322 

96129 

30-4 

IH57 

95406 

25  5 

09359 

96115 

30-5 

11194 

95392 

25.6 

09395 

96100 

30.6 

11230 

95378 

25  7 

09432 

96086 

30-7 

11267 

95363 

25.8 

09469 

96071 

30.8 

11304 

95349 

25  9 

09505 

96057 

30-9 

11340 

95335 

26.0 

09542 

96042 

31  o 

H377 

95320 

i, 

9,      —10 

i, 

9,      —  io 

26.1 

09579 

96027 

31.1 

11414 

95306 

26.2 

09615 

96013 

31  2 

11450 

95292 

263 

09652 

95998 

3i  3 

11487 

95278 

26.4 

09689 

95984 

3i  4 

11524 

95263 

26.5 

09726 

95969 

3i  5 

11561 

95249 

26.6 

09762 

95955 

31-6 

H597 

95235 

26.7 

09799 

95940 

3i  7 

11634 

95220 

26.8 

09836 

95925 

31-8 

11671 

95206 

26.9 

09872 

95901 

3i-9 

11707 

95192 

27.0 

09909 

95897 

32.0 

11744 

95178 

i, 

9,      —  10 

i, 

9,      —  io 

27.1 

09946 

95882 

32.1 

11781 

95163 

27.2 

09982 

95868 

32.2 

11817 

95H9 

27  3 

10019 

95853 

32  3 

11854 

95135 

27.4 

10056 

95839 

32-4 

11891 

95120 

27  5 

10093 

95824 

32-5 

11928 

95106 

27.6 

10129 

95810 

32.6 

11964 

95092 

27.7 

10166 

95795 

32-7 

I2OOI 

95078 

27-8 

10203 

9578i 

32-8 

12038 

95064 

27.9 

10239 

95767 

32-9 

12074 

95049 

28.0 

10276 

95752 

33  o 

I2III 

95035 

I, 

9,      —  10 

If 

9,      —  io 

28.1 

10313 

95737 

33  i 

12148 

95021 

28.2 

10349 

95723 

33  2 

12184 

95007 

28.3 

10386 

95709 

33  3 

I222I 

94993 

28.4 

10423 

95694 

33  4 

12258 

94978 

28.5 

10460 

95679 

33  5 

12295 

94964 

28  6 

10496 

95665 

33  6 

I233I 

94950 

28  7 

10533 

95651 

33  7 

12368 

94936 

28.8 

10570 

95636 

33-8 

12405 

94922 

28.9 

10606 

95622 

33  9 

12441 

94907 

29.0 

10643 

956o8 

34  o 

12478 

94893 

410 


Tension  of  Aqueous  Vapor 

Expressed  in  millimeters  of  mercury  at  o°,  density  of  mercury 

=  13.59593  at  latitude  45°  and  at  the  sea-level 
Calculated  from  Regnault's  measurements  by  Broch  (Trav.  et 
Mem.  du  Bur.  intern,  des  Poids  et  Mes.  I  A.  33,  1881) 


1 

Tension 

t 

Tension 

t 

Tension 

t 

Tension 

mm. 

mm. 

mm. 

mm. 

—  2°.0 

3  •  9499 

2°.  6 

5  •  5008 

7°.  i 

7.5I7I 

11°.  6 

10.1614 

—1.9 

3.9790 

2-7 

5-5398 

7-2 

7.5685 

11.7 

10.2285 

—1.8 

4.0082 

2.8 

5-5790 

73 

7.6202 

ii.  8 

10.2960 

—  -7 

4.0376 

2.9 

5-6185 

74 

7.6722 

11.9 

10.3639 

—  .6 

4.0672 

30 

5.6582 

75 

7.7246 

12.  0 

10.4322 

—  -5 

4.0970 

7.6 

7-7772 

4.1271 

31 

5-6981 

7-7 

7.8302 

12.  1 

IO  .  5009 

—  3 

4-1574 

32 

5.7383 

7.8 

7-8834 

12.2 

10.5700 

—  .2 

4-1878 

33 

5.7788 

79 

7.9370 

12.3 

10.6394 

—  .1 

4.2185 

34 

5-8I95 

8.0 

7.9909 

12.4 

10.7093 

35 

5-8605 

12-5 

10.7796 

—  I.O 

4  •  2493 

36 

5-90I7 

8.1 

8.0452 

12.6 

10.8503 

—  O  .  Q 

4  .  2803 

3-7 

5-9432 

8.2 

8.0998 

12.7 

10.9214 

o 

—  o  .  o 

4.3116 

38 

5-9850 

8-3 

8.1547 

12.8 

10.9928 

—0.7 

4-3430 

39 

6.0270 

8-4 

8.2099 

12.9 

II  .0647 

—0.6 

4-3747 

4.0 

6.0693 

8-5 

8.2655 

13  o 

11.1370 

—  °  5 

4.4065 

8.6 

8.3214 

—0.4 

4.4385 

4-1 

6.III8 

8.7 

8-3777 

I3-I 

11.2097 

—03 

4.4708 

4.2 

6.1546 

8.8 

8.4342 

13  2 

11.2829 

—  0.2 

4-5032 

43 

6-1977 

8.9 

8.4911 

13  3 

H.3564 

—  O.I 

4-5359 

44 

6.2410 

9.0 

8.5484 

13  4 

11.4304 

45 

6  .  2846 

13  5 

11.5048 

o.o 

4-5687 

4.6 

6.3285 

13  6 

11-5797 

+  0.1 

4.6017 

47 

6.3727 

9-1 

8.  6061 

13  7 

11.6550 

0.2 

4-6350 

4.8 

6.4171 

9.2 

8.6641 

13-8 

11.7307 

0-3 

4.6685 

49 

6.4618 

93 

8.7224 

13  9 

11.8069 

0.4 

4.7022 

5.0 

6.5067 

94 

8.7810 

14.0 

11.8835 

05 

4.  7361 

8.8400 

0.6 

4-7703 

9.6 

8.8993 

0.7 

4  .  8047 

5.1 

6.5519 

97 

8.9589 

14.1 

11.9605 

0.8 

4.8393 

52 

6-5974 

9-8 

14.2 

12.0380 

0.9 

4.8741 

53 

6.6432 

99 

9.0792 

14  3 

12.1159 

I.O 

4.9091 

5-4 

6.6893 

IO.O 

9.1398 

14.4 

12.1943 

55 

6-7357 

14-5 

12.2731 

.1 

4-9443 

56 

6.7824 

IO.I 

9.2009 

14.6 

12.3523 

.2 

4.9798 

57 

6.8293 

IO.2 

9.2623 

14-7 

12.4320 

3 

5-0155 

5-8 

6.8765 

10.3 

9.3241 

14.8 

12.5122 

4 

5-0515 

59 

6.9240 

10.4 

9-3863 

14  9 

12.5928 

•  5 

5-0877 

6.0 

6.9718 

IO.5 

9.4488 

15-0 

12.6739 

.6 

5.1240 

10.6 

9.5117 

7 

5.1606 

6.1 

7.0198 

10.7 

9-5750 

15-1 

12-7554 

.8 

5.1975 

6.2 

7.0682 

10.8 

9.6387 

15  2 

12.8374 

9 

5.2346 

6-3 

7.1168 

10.9 

9.7027 

15  3 

12.9198 

.0 

5-27I9 

6.4 

7-1658 

II.  0 

9.7671 

15  4 

13.0027 

6-5 

7.2150 

15  5 

13.0861 

2.1 

5.3094 

6.6 

7  .  2646 

ii.  i 

9.8318 

15  6 

13.1700 

2.2 

5-3472 

6.7 

7.3145 

II.  2 

9.8969 

15  7 

I3-2543 

23 

5-3852 

6.8 

7-3647 

11.3 

9.9624 

15-8 

I3.3392 

2-4 

5.4235 

69 

7-4152 

II  .4 

10.0283 

15  9 

I3-4245 

2-5 

5.4620 

7.0 

7.4660 

ii  5 

10.0946 

16.0 

I3-5I03 

Tension  of  Aqueous  Vapor.  —  Continued 


I      Tension 

t 

Tension 

/     Tension 

/ 

Tension 

mm. 

mm. 

mm. 

mm. 

i6°.i 

I3-5965 

20°.  6 

18.0176 

25°-  1 

23-6579 

29°.  6 

30.7928 

16.2 

13.6832 

20.7 

18.1288 

25-2 

23.7991 

29.7 

30.9707 

16.3 

I3-7705 

20.8 

18.2406 

25  3 

23.9411 

29.8 

31.1494 

16.4 

13.8582 

20.9 

18.3529 

25  4 

24.0838 

29.9 

31.3291 

16.5 

13.9464 

21.0 

18.4659 

25  5 

24.2272 

30.0 

31.5096 

16.6 

I4-035I 

25-6 

24.3714 

167 

14.1243 

21.  1 

18.5795 

25  7 

24.5164 

30.1 

31.6910 

16.8 

14.2141 

21.2 

18.6937 

25-8 

24.6620 

30.2 

3I-8734 

16.9 

I4-3043 

21.3 

18.8085 

25  9 

24  .  8084 

30.3 

32-0567 

17.0 

I4-3950 

21.4 

18.9240 

26.0 

24-9556 

30.4 

32.2410 

21-5 

19.0400 

30-5 

32.4262 

17.1 

14.4862 

21.6 

19.1567 

26.1 

25.1035 

30.6 

32.6124 

17.2 

14-5779 

21-7 

19.2740 

26.2 

25-2523 

30.7 

32-7995 

17  3 

14.6702 

21.8 

19.3920 

26.3 

25.4018 

30.8 

32.9875 

17  4 

14.7630 

21.9 

I9-SI05 

26.4 

25.5521 

30.9 

33-I765 

17  5 

14.8563 

22.0 

19.6297 

26.5 

25.7032 

31.0 

33-3664 

17.6 

14.9501 

26.6 

25-855I 

17.7 

15.0444 

22.1 

19.7496 

26.7 

26.0077 

31-1 

33-5573 

17-8 

I5-I392 

22.2 

19.8701 

26.8 

26.l6l2 

31  2 

33-7491 

17.9 

I5-2345 

22.3 

19.9912 

26.9 

26^155 

31-3 

33.94I9 

18.0 

15.3304 

22.4 

2O.  1130 

27.0 

26.4705 

3i  4 

34-I356 

22.5 

20.2355 

3i  5 

34-3303 

18.1 

15.4268 

22.6 

20.3586 

27.1 

26.6263 

31-6 

34-5259 

18.2 

I5-5237 

22.7 

20.4824 

27.2 

26.7830 

31-7 

34-7225 

18.3 

15.6212 

22.8 

20.6068 

27  3 

26  .  9405 

31-8 

34.9201 

18.4 

15.7192 

22.9 

20.7319 

27.4 

27.0987 

3i  9 

35.1186 

18.5 

15.8178 

23.0 

20.8576 

27  5 

27.2578 

32.0 

35-3i8i 

18.6 

15.9169 

27.6 

27.4177 

18.7 

16.0166 

23.1 

20.9840 

27.7 

27-5784 

32.1 

35-5i86 

18.8 

16.1168 

23.2 

2I.IIIO 

27.8 

27-7399 

32.2 

35.7201 

18.9 

16.2176 

23  3 

21.2388 

27.9 

27.9023 

32-3 

35.9226 

19.0 

16.3189 

23  4 

21.3672 

28.0 

28.0654 

32.4 

36.1261 

23  5 

21.4964 

32-5 

36-3307 

19.1 

16.4208 

23.6 

21.6262 

28.1 

28.2294 

32  6 

36-5363 

19.2 

16.5233 

23  7 

21.7567 

28.2 

28.3942 

32-7 

36.7429 

iQ  3 

16.6263 

23.8 

21.8879 

28.3 

28.5599 

32.8 

36-9505 

19.4 

16.7299 

23  9 

22.0198 

28.4 

28.7265 

32  9 

37-1592 

19  5 

16.8341 

24.0 

22.1524 

28.5 

28.8939 

33  -o 

37-3689 

19-6 

16.9388 

28.6 

29.0622 

19.7 

17.0441 

24.1 

22.2857 

28.7 

29.2313 

33  i 

37-5796 

19.8 

17.1499 

24.2 

22.4196 

28.8 

29.4013 

33  2 

37-79H 

19.9 

17.2563 

24  3 

22-5543 

29.9 

29.5722 

33  3 

38.0042 

20.0 

17-3632 

24.4 

22.6898 

29.0 

29.7439 

33  4 

38.2180 

24  5 

22.8259 

33  5 

38.4329 

2O.  I 

17.4707 

24.6 

22.9628 

29.1 

29.9165 

33  6 

38.6488 

20.2 

17-5789 

24-7 

23  .  1003 

29.2 

30.0900 

33-7 

38-8657 

20.3 

17.6877 

24.8 

23.2386 

29  3 

30.2644 

33  8 

39-o837 

20.4 

17.7971 

24.9 

23-3777 

29.4 

30.4396 

33  9 

39.3027 

20.5 

17.9071 

25.0 

23-5I74 

29  5 

30.6157 

34  -o 

39.5228 

412 


INDEX  OF  AUTHORS'  NAMES 


Albrecht,  determination  of  naph- 
thalene, 260 

Allen,  applications  of  Lunge  ni- 
trometer, 397 

Anderson,  combustion  of  gases, 
127;  determination  of  carbon 
dioxide  in  air,  387 

Andrews,  detection  of  ozone,  172; 
determination  of  hydrogen  cya- 
nide, 269 

Anneler,  determination  of  ozone, 
179,  181 

Arago,  refraction  of  gases,  305 

Arndt,  determination  of  nitrous 
oxide,  214;  methane  in  acety- 
lene, 269 

Arnold,    detection    of    ozone,    172, 

173, 174 
August,  psychrometer,  375 

B 

Bamberger,    evaluation    of    calcium 

carbide,  363 

Barreswill,  detection  of  ozone,  172 
Bartlett,    determination    of    carbon 

monoxide     with     iodine     pentox- 

ide,  237 
Baskerville,  determination  of  nitrous 

oxide,  215 

Beagle,  heating  value  of  coal,  335 
Benedict,    preparation    of    alkaline 

pyrogallol,    160;    composition    of 

the  atmosphere,  371;  relation  of 

carbon     dioxide     to     oxygen     in 

air,  377 


Bernthsen,  hyposulphurous  acid.  168 
Biot,  refraction  of  gases,  304 
le    Blanc,   absorption   of   nitric   ox- 
ide, 218 
Bleier,  apparatus  for  carbon  dioxide 

in  air,  387 

Bodlander,  gas  baroscope,  40 
Boettger,  detection  of  ozone,  172 
Broch,  tension  of  aqueous  vapor,  411 
Brunck,     absorption    of    hydrogen, 
184;     fractional     combustion     of 
hydrogen,  194 

Briinnich,  detection  of  cyanogen,  263 
Bunsen,  collection  of  gases  from 
springs,  15;  collection  of  gases 
dissolved  in  water,  19;  collection 
of  gases  from  reactions  in  sealed 
tubes,  21 ;  determination  of  specific 
gravity  of  a  gas,  44;  proportion 
of  gases  in  analysis  by  explosion, 
143;  oxy hydrogen  gas  generator, 
145;  hydrogen  apparatus,  159; 
solubility  of  hydrogen  in  alcohol, 
181;  solubility  of  nitrogen  in 
water,  206;  solubility  of  methane 
in  water,  240;  solubility  of  ethylene 
in  water,  248;  solubility  of  hydro- 
gen sulphide,  270;  determination 
of  chlorine,  285;  photometer,  308 
Bunte,  gas  burette,  74;  combustion 
of  hydrogen  with  palladium,  192 


Carius,  solubility  of  oxygen  in  alco- 
hol, 158;  solubility  of  nitrogen  in 
alcohol,  207;  solubility  of  nitrous 


413 


414 


INDEX  OF  AUTHORS'  NAMES 


oxide,  213;  solubility  of  nitric 
oxide  in  alcohol,  217;  solubility 
of  ethylene  in  alcohol,  249 

Caro,  sulphur  compounds  in  crude 
acetylene,  368 

de  Castro,  fractional  combustion  of 
hydrogen,  200 

Cedercreutz,  determination  of  phos- 
phorus in  acetylene,  358 

Centnerszwer,  absorption  of  oxygen 
by  phosphorus  in  solution,  166 

Chapman,  brass  suction  pump,  8 

Christie,  determination  of  chlo- 
rine, 286 

Clausman,  absorption  of  carbon 
monoxide,  234 

Collie,  automatic  device  for  circula- 
tion of  gas,  209 

Colman,  determination  of  naphtha- 
lene, 260 

Coquillion,  combustion  pipette,  147; 
combustion  with  metallic  palla- 
dium, 192 

Crum,  reduction  of  oxides  of  nitro- 
gen by  mercury,  393 


Davies,  determination  of  benzene, 
258 

Davis,  determination  of  nitric  oxide, 
222 

Denham,  combustion  of  methane, 
194 

Dennis,  gas  absorption  pipette,  81; 
modified  -form  of  Orsat  apparatus, 
86;  combustion  of  gases  in  com- 
bustion pipette,  153;  absorption 
of  benzene  by  alcohol,  253;  ab- 
sorption of  benzene  with  nickel 
solution,  255;  determination  of 
phosphorus  in  acetylene,  360;  mod- 
ified Hempel  nitrometer,  393 


Dennstedt,  absorption  of  oxygen  by 
chromous  chloride,  169 

Dittmar,  collection  of  gases  dis- 
solved in  water,  19;  solubility  of 
hydrogen  chloride,  289 

Divers,  determination  of  nitric  ox- 
ide, 219 

Doepner,  detection  of  carbon  mon- 
oxide in  blood,  231 

Doyere,  gas  pipette,  53,  105;  ap- 
paratus for  gas  analysis,  99 

Drehschmidt,  platinum  combustion 
pipette,  154;  absorption  of  carbon 
monoxide  by  cuprous  chloride, 
233;  determination  of  total  sul- 
phur, 319 

Dulong,  refraction  of  gases,  304 

von  Dumreicher,  determination  of 
nitrous  oxide,  214 

Dupasquier,  determination  of  hydro- 
gen sulphide,  272 

E 

Eckardt,  properties   of   Griess's   re- 
agent, 218;  reaction  of  arsine  and 
silver   nitrate,    292;    detection   of 
arsine,  293 
Eitner,  determination  of  phosphorus 

in  acetylene,  358 
Engler,  detection  of  ozone,  172 
Erlwein,  detection  of  ozone,   172 
Ettling,  gas  pipette,  53,  100,  105 


Feder,  determination  of  sulphur  in 

coal  gas,  323 
Fisher,   Franz,   detection    of   ozone, 

173;  absorption  of  nitrogen,  209, 

211,  212 
Fraenkel,   amount   of  phosphine   in 

crude  acetylene,  357;  determina- 


INDEX  OF  AUTHORS'  NAMES 


tion  of  phosphorus,  in  acetylene, 
358;  silicon  hydride  in  crude 
acetylene,  368 

Franzen,  furnace  sampling  tube,  i; 
glass  sampling  tube,  7;  absorption 
of  oxygen  by  sodium  hyposulphite, 
168,  169 

Fresenius,  combustion  of  hydro- 
carbons, 198;  determination  of  hy- 
drogen sulphide,  272;  determina- 
tion of  chlorine  and  hydrochloric 
acid,  288 

Friedrichs,  spiral  gas  washing  bottle, 
81,  123 

Frischer,  preparation  of  cuprous 
chloride,  233 

Fritzsche,  separation  of  ethylene 
from  butylene,  250;  determination 
of  naphthalene,  260 


Gair,  determination  of  naphthalene, 
260 

Ganassini,  detection  of  hydrogen 
sulphide,  271 

Gautier,  absorption  of  carbon  mon- 
oxide, 234;  determination  of  carbon 
monoxide  with  iodine  pentoxide, 

235 

Genzken,  autolysator,  303 

Gill,  determination  of  carbon  mon- 
oxide with  iodine  pentoxide,  237 


Haber,  manipulation  of  Bunte  bu- 
rette, 78;  absorption  of  ethylene 
by  bromine,  249;  separation  of 
ethylene  from  benzene,  250;  sepa- 
ration of  benzene  from  ethylene, 
255;  determination  of  benzene, 
258;  gas  refractometer,  304 


Hahn,  position  of  burette  in  Orsat 

apparatus,  84 

Hahnei,  absorption  of  nitrogen,  211 
Haldane,  colorimetric  determination 

of  carbon  monoxide,  237 
Harbeck,  determination  of  benzene, 

254 

Harding,  determination  of  benzene, 
258;  burner  for  sulphur  determina- 
tion, 323 

de  la  Harpe,  detection  of  carbon 
monoxide,  231 

Hartmann,  absorption  of  hydro- 
gen, 182 

Hassler,  absorption  of  oxygen  by 
chromous  chloride,  169 

Hempel,  air  sampling  tubes,  3; 
simple  gas  burette,  51;  absorption 
apparatus,  53;  absorption  of  oxy- 
gen and  carbon  monoxide,  78; 
burette  with  correction  tube,  90; 
mercury  absorption  apparatus,  96; 
apparatus  for  exact  gas  analysis, 
99;  explosion  pipette,  142;  oxy- 
hydrogen  gas  generator,  145; 
hydrogen  pipette,  145;  explosion 
pipette  for  exact  analysis,  146; 
hydrogen  pipette  for  exact  analy- 
sis, 147;  absorption  of  oxygen  by 
pyrogallol,  160;  absorption  of  hy- 
drogen by  colloidal  palladium,  185; 
absorption  of  hydrogen  by  palla- 
dium black,  1 88;  palladium  sponge, 
193;  determination  of  hydrogen 
with  palladium  asbestos,  195; 
fractional  combustion  of  hydrogen 
with  palladium  black,  196;  ab- 
sorption of  nitrogen  by  various 
substances,  207;  determination 
of  nitrous  oxide,  214;  combustion 
of  methane  in  combustion  pipette, 
246;  absorption  of  benzene  by 


4i6 


INDEX  OF  AUTHORS'  NAMES 


alcohol,  253;  absorbents  for  carbon 
oxysulphide,  278;  determination  of 
carbon  oxysulphide,  279;  determi- 
nation of  fluorine,  280;  nitro- 
meter, 393 

Henry,  fractional  combustion  of  hy- 
drogen, 192 

Hesse,  carbon  dioxide  in  air,  377 
Hoffman,  furnace  sampling  tube,  i; 

glass  sampling  tube,  7 
Hofmann,  ammonia  benzene  nickel 

cyanide,  255 

Honigmann,  gas  burette,  72 
Hopkins,    combustion    of    gases    in 

combustion  pipette,  153 
Hopp,  sulphur  in  coal  gas,  324 
Hoppe-Seyler,    collection    of    gases 

dissolved  in  water,  19 
Houzeau,  detection  of  ozone,  171 
Hulett,  distillation  of  mercury,  117 
Huntly,  gas  sampling  tube,  5 


Ilosvay,  Griess's  reagent,  218 


Jacobsen,  removal  of  carbon  dioxide 
from  water,  21 

Jager,  fractional  combustion  of  hy- 
drogen, 198 

Johoda,  autolysator,  303 

von  Jolly,  determination  of  oxygen, 

159 

Jorissen,  determination  of  naphtha- 
lene, 260 

Junkers,  gas  calorimeter,  347;  auto- 
matic gas  calorimeter,  354 


Kampschulte,  detection  of  ozone,  1 73 
Keiser,  detection  of  ozone,  171 


Kellner,  heating  value  of  liquid  fuel, 
347 

Keppeler,  carbon  monoxide  in  acety- 
lene, 355;  determination  of  phos- 
phorus in  acetylene,  358;  deter- 
mination of  carbon  monoxide 
in  acetylene,  369. 

Keyes,  collection  of  gas  from  mer- 
cury pump,  13;  lubricant  for  stop- 
cocks, 116 

Kinnicutt,  determination  of  carbon 
monoxide  with  iodine  pentoxide, 

235 

Klason,  carbon  oxysulphide,  278 

von  Knorre,  fractional  combustion 
of  hydrogen,  199;  determination 
of  nitrous  oxide,  214;  methane 
in  acetylene,  369 

Kohn-Abrest,  removal  of  oxygen 
from  air,  230 

Kopfer,  platinum  asbestos,  193 

Korting,  steam  aspirator,  8 

Kostin,  absorption  of  oxygen  by 
ferrous  salts,  168;  removal  of  oxy- 
gen from  air,  229 

Kreidl,  determination  of  sulphur 
dioxide,  276 

Kreusler,  determination  of  oxygen, 

iS9 

Kunkel,  detection  of  carbon  mon- 
oxide in  blood,  231 

Kunz-Krause,  detection  of  cyanogen, 
262,  263 

Kiispert,  ammonia  benzene  nickel 
cyanide,  255 


Lassaigne,  reaction    of    arsine    and 

silver  nitrate,  292 

Lemoult,  detection  of  phosphine,  291 
Levy,  detection  of  carbon  monoxide, 

231 


INDEX  OF  AUTHORS'  NAMES 


417 


Lewes,  determination  of  ammonia  in 
crude  acetylene,  357 

Liebenthal,  photometry,  305 

Limpricht,  reduction  of  dinitroben- 
zene,  255 

Lindemann,  absorption  of  oxygen 
by  solid  phosphorus,  163 

Lloyd,  hygrodeik,  375 

Lockemann,  properties  of  Griess's 
reagent,  218;  reaction  of  arsine 
and  silver  nitrate,  292;  detection 
of  arsine,  293 

Lundstrom,  carbon  monoxide  in  acet- 
ylene, 369 

Lunge,  gas  volumeter,  37;  detection 
of  nitrous  oxide,  213;  preparation 
of  Griess's  reagent,  218;  determina- 
tion of  nitric  oxide,  220,  222; 
determination  of  benzene,  254; 
determination  of  sulphur  dioxide, 
275;  determination  of  carbon 
oxysulphide,  279;  ten-bulb  tube, 
359;  nitrometer,  393,  397 


M 

McCarthy,  determination  of  ben- 
zene, 256 

McMaster,  detection  of  ozone, 
171 

McWhorter,  determination  of  carbon 
monoxide  with  iodine  pentoxide, 

235 

Manchot,  detection  of  ozone,  173 
Marx,  detection  of  ozone,  173 
Mentzel,    detection   of   ozone,    172, 

173,  174 
Misteli,  determination  of  hydrogen 

by  explosion,  144,  186 
Moissan,    preparation    of    chromous 

chloride,   169;  hydrogen   sulphide 

in  crude  acetylene,  367 


Moody,  determination  of  ethylene, 

249 
Morgan,    determination    of    carbon 

monoxide  with  iodine  pentoxide, 

235 
Moser,  determination  of  nitric  oxide, 

219,  220,  222 
Miiller,  absorption  of  benzene,  254; 

determination  of  naphthalene,  260 


N 

Naccari,  solubility  of  carbon  dioxide, 
225 

Nauss,  determination  of  cyanogen, 
263 

Nesmjelow,  fractional  combustion 
of  hydrogen,  195;  preparation  of 
palladium  asbestos,  195;  fractional 
combustion  of  carbon  monoxide, 

239 

Nicloux,  determination  of  carbon 
monoxide  with  iodine  pentoxide, 

235 

Nowicki,  determination  of  carbon 
monoxide  with  iodine  pentoxide, 
235 


O'Brien,  determination  of  phos- 
phorus in  acetylene,  358 

Oechelhauser,  absorption  of  ethy- 
lene by  bromine,  249;  separation 
of  ethylene  from  benzene,  250; 
separation  of  benzene  from  ethy- 
lene, 255 

Oettel,  determination  of  fluorine,  280 

Offerhaus,  suction  device,  8;  determi- 
nation of  chlorine,  285 

Ogier,  removal  of  oxygen  from  air, 
230 


4i8 


INDEX  OF  AUTHORS'  NAMES 


O'Neill,   determination   of   benzene, 

253,  255 
Orsat,  apparatus  for  gas  analysis,  78 


Paal,  absorption  of  hydrogen,   182 

Pagliani,  solubility  of  carbon  dioxide, 
225 

Palmqvist,  determination  of  carbon 
dioxide  in  air,  382 

Pannertz,  determination  of  specific 
gravity  of  gases,  47 

Paul,  vitiation  of  air,  376 

Pecoul,  detection  of  carbon  mon- 
oxide, 231 

Petschek,  absorption  of  hydrogen, 
1 86 

Pettenkofer,  carbon  dioxide  in  air, 

377 

Pettersson,  removal  of  carbon  diox- 
ide from  water,  21;  compensating 
tube,  90;  solubility  of  oxygen  in 
water,  158;  solubility  of  nitrogen 
in  water,  207;  determination  of 
carbon  dioxide  in  air,  382 

Pfeifer,  manipulation  of  Orsat  ap- 
paratus, 84 

Pfeiffer,  determination  of  benzene, 
254,  258 

von  der  Pfordten,  preparation  of 
chromous  chloride,  169 

Phillips,  detection  of  hydrogen,  181 

Preusse,  collection  of  gases  dis- 
solved in  liquids,  16 


Raken,     determination     of     carbon, 
monoxide  with  iodine  pentoxide, 

237 
Ramsey,    collection   of    gases    from 


springs,  15;  collection  of  gases 
from  minerals,  22 

Raschig,  determination  of  sulphur 
dioxide  in  presence  of  nitrous  acid, 
276 

Reckleben,  properties  of  Griess's  re- 
agent, 218;  reaction  of  arsine  and 
silver  nitrate,  292;  detection  of 
arsine,  293 

Regnault,  tension  of  aqueous  vapor, 
411. 

Reich,  determination  of  sulphur 
dioxide,  274 

Reichardt,  collection  of  gases  dis- 
solved in  liquids,  16 

Reinhardt,  confining  liquid  in  gasom- 
eters, 26 

Reverdine,  detection  of  carbon  mon- 
oxide, 231 

Rhodes,  efficiency  of  absorption 
apparatus,  81;  formation  of  oxides 
of  nitrogen  in  combustion  pipette, 
153;  detection  and  determination 
of  cyanogen,  265 

Richardt,  fractional  combustion  of 
hydrogen,  193,  194 

Ringe,  absorption  of  nitrogen,  212 

Rolland,  apparatus  for  determina- 
tion of  carbon  dioxide,  78 

Rosa,  photometric  units,  307;  heat- 
ing value  of  gaseous  fuels,  352 

Roscoe,  solubility  of  hydrogen  chlo- 
ride, 289 

Rossel,  methane  in  acetylene,  369 

Rutten,  determination  of  naphtha- 
lene, 260 


Samtleben,  cyanogen  in  gas,  265 
Sandmeyer,  preparation  of  cuprous 

chloride,  232 
Sandriset,  methane  in  acetylene,  369 


INDEX  OF  AUTHORS'  NAMES 


419 


Sanford,  determination  of  carbon 
monoxide  with  iodine  pentoxide, 

235 

Saussure,  carbon  dioxide  in  air,  377 

Schaer,  detection  of  cyanogen,  262 

Scheffier,  determination  of  fluorine, 
280 

Scheiber,  determination  of  acety- 
lene, 252 

Scheurer-Kestner,  combustion  of  hy- 
drocarbons, 198 

Schilling,  determination  of  specific 
gravity  of  gases,  46 

Schlosing,  apparatus  for  determina- 
tion of  carbon  dioxide,  78 

Schonbein,  detection  of  ozone,  171, 
172;  determination  of  nitric  oxide, 
221 

Schonbein-Pagenstecher,  detection  of 
cyanogen,  262 

Schoene,  detection  of  ozone,  172 

Schoenn,  detection  of  ozone,  172 

Schonfeld,  solubility  of  chlorine,  285 

Schumacher,  determination  of  sul- 
phur in  coal  gas,  323 

Schutzenberger,  hyposulphurous 
acid,  1 68 

Simmance-Abady,  carbon  dioxide 
recorder,  300 

Sims,  solubility  of  sulphur  dioxide, 

273 

de  Smet,  combustion  of  gases,  127 

Smith,  determination  of  naphtha- 
lene, 260 

Smits,  determination  of  carbon  mon- 
oxide with  iodine  pentoxide,  237 

Sonden,  solubility  of  oxygen,  158; 
solubility  of  nitrogen,  207 

Stavorinus,  determination  of  ben- 
zene, 258,  260 

Stevenson,  determination  of  nitrous 
oxide,  215 


Stockmann,  combustion  of  hydro- 
carbons, 198 

Stokes,  absorption  of  ethylene  by 
bromine,  249 

Strache,  autolysator,  303 

Struve,  detection  of  ozone,  172 


Tait,  detection  of  ozone,  172 

Taylor,  determination  of  benzene, 
258 

Teclu,  explosive  limits  of  gas  mix- 
tures, 143 

Terreil,  determination  of  nitric  oxide, 

220 

Tiemann,  collection  of  gases  dis- 
solved in  liquids,  16 

Timofejew,  solubility  of  hydrogen, 
181 

Topler,  mercury  pump,  9 

Torwogt,  determination  of  carbon 
monoxide  with  iodine  pentoxide, 

237 
Travers,  Topler  pump,  9;  collection 

of  gases  from  mineral  waters,  15; 

collection  of  gases  from  minerals, 

22;  removal  of  nitrogen  from  the 

air,  209 
Treadwell,  determination  of  ozone, 

179,   181;  absorption  of  ethylene 

by  bromine,  249;  determination  of 

chlorine,  285,  286 
Tucker,  determination  of  ethylene, 

249 

U 

Ubbelohde,  fractional  combustion 
of  hydrogen,  200 


Vogel,  solubility  of  acetylene,  250; 
phosphine  in  crude  acetylene,  357 


420 


INDEX  OF  AUTHORS'  NAMES 


Voigt,  confining  liquid  in  gasometers, 

26 

de  Voldere,  combustion  of  gases,  127 
Volhard,  determination  of  silver,  289 

W 

Wagner,    determination    of    nitrous 

oxide,  214 

Wallis,  detection  of  cyanogen,   265 
Watts,  reduction  of  oxides  of  nitro- 
gen by  mercury,  393 
Weil,  detection  of  ozone,  172 
Weiskopf,   determination  of  carbon 
monoxide  with  iodine  pentoxide, 

235 

White,  formation  of  oxides  of  nitro- 
gen in  combustion  pipette,  152 

Wild,  detection  of  ozone,  172 

Wilfarth,  determination  of  nitric 
oxide,  222 

Winkler,  Clemens,  gas  sampling  tube, 
i;  gas  burette,  70;  absorption  ap- 
paratus, 124;  combustion  pipette, 
147;  platinum  combustion  tube, 
155;  palladium  asbestos,  193; 


fractional  combustion  with  palla- 
dium asbestos,  194;  cuprous  chlo- 
ride, 232;  determination  of  hydro- 
gen chloride,  289 

Winkler,  L.  W.,  solubility  of  oxygen, 
158;  solubility  of  hydrogen,  181; 
solubility  of  carbon  monoxide, 
226 

Witzeck,  solubility  of  carbon  oxy- 
sulphide,  278;  determination  of 
carbon  oxysulphide,  279 

Wohl,  molecular  volumes  of  certain 
gases  as  influencing  combustion 
analysis,  139 

Wolff,  absorption  tube,  227;  hydro- 
gen sulphide  in  crude  acetylene, 
367 

Wurster,  detection  of  ozone,  171,  174 


Young,    determination    of    sulphur 
in  coal  gas,  327 


Zenghelis,  detection  of  hydrogen,  182 


INDEX  OF  SUBJECTS 


Absolute  humidity,  371 
Absorbing  power,  analytical,  of  re- 
agents, 65 

Absorbing  power  of  a  reagent,  de- 
termination of,  65 
Absorption  apparatus  for  use  with 

large  volumes  of  gas,  122 
Absorption  apparatus,  Winkler,  124 

Winkler-Dennis,  125 
Absorption   of   gases   with   Hempel 

pipettes,  6 1 
Absorption  of  oxygen  with  alkaline 

pyrogallol,  161 
Absorption  pipette,  double,  for  liquid 

reagents,  Hempel,  56 
simple,     for     liquid     reagents, 

Hempel,  53 

double,  for  solid  and  liquid  re- 
agents, Hempel,  58 
simple,  for  solid  and  liquid  re- 
agents, Hempel,  55 
Hankus,  79 
Heinz,  80 
Nowicki,  80 
Absorption  pipettes,  efficiency  of,  81 

for  mercury,  96 
Acetylene,  250 

absorption  of,  251 

amount  of  phosphine  in  crude, 

357 

commercial,  analysis  of,  356 
commercial,  impurities  in,  355 
determination   of  ammonia   in, 
356 


determination  of,  by  absorp- 
tion with  cuprous  chloride, 
252 

determination  of,  by  absorp- 
tion with  fuming  sulphuric 
acid,  252 

determination  of,  by  combus- 
tion, 251 

determination  of  carbon  mon- 
oxide in,  369 

determination  of  hydrogen  in, 
356 

determination  of  oxygen  and 
nitrogen  in,  369 

determination  of  phosphine  in, 
357 

determination    of    methane    in, 

369 

determination  of  silicon  hydride 
in,  368 

determination  of  sulphur  in,  367 

from  calcium  carbide,  deter- 
mination of  yield  of,  363 

from  pure  calcium  carbide, 
volume  of,  363 

generation  of,  from  calcium  car- 
bide, 361 

separation  of,  from  ethylene,  249 

solvents  for,  250 
Air  (see  Atmospheric  air) 
Ammonia,  224 

detection  of,  224 

detection  of,  by  Nessler's  re- 
agent, 224 

determination  of,  224 


421 


422 


INDEX  OF  SUBJECTS 


Ammonia    in   acetylene,  determina- 
tion of,  356 

Ammonia   nickel    cyanide,    prepara- 
tion of  solution  of,  256 
Ammoniacal  silver  solution,  prepara- 
tion of,  249 

Amylacetate  lamp,  307 
Analyses    with    Hempel    apparatus, 
accuracy  of,  67 
by  combustion,  147 
by  explosion,  141 
by  explosion,  proportion  of  gases 

in,  143 
with    water    as    the    confining 

liquid,  51 

Analytical   absorbing   power   of   re- 
agents, 65 

Anderson's  apparatus  for  determina- 
tion of  carbon  dioxide  in  air,  387 
Apparatus,  absorption,  for  use  with 

large  volumes  of  gas,  122 
absorption,  Winkler,  124 
absorption,  Winkler-Dennis,  125 
connection  of,  113 
construction  of,  113 
for  analysis  with  water  as  con- 
fining liquid,  51 
for  exact  analysis  over  mercury, 

Hempel,  90 
mounting  of,  114 
Orsat,  78 

without  stopcocks,  Hempel,  99 
Aqueous  vapor,  tension  of,  411 
Argon,  213 

group,  gases  of,  213 

group,    separation    of    nitrogen 

from,  209,  212 

Arrangement  of  laboratory,  49 
Arsine,  291 

detection  of,  293 
reaction  of,  with  silver  nitrate, 
292 


Asbestos,  palladium,  preparation  of, 

195 
Aspirator,  glass  bottle,  7 

rubber  bulb,  7 

steam,  8 

water  suction  pump,  8 
Atmospheric  air,  analysis  of,  370 

collection  of  samples  of,  3 

composition  of,  370 

detection  of  ozone  in,  1 78 

determination  of  carbon  dioxide 
in,  376 

determination    of    moisture    in, 

37i 

determination  of  nitrites  in,  222 
examination  of,  370 
removal  of  oxygen  from  large 

volume  of,  229 
Atomic  weights,  405 
August  psychrometer,  375 
Autolysator    for    determination    of 

carbon  dioxide,  302 
Automatic  flue  gas  analysis,  299 

gas  calorimeter,  354 
Average  sample,  collection  of,  5 

B 

Baroscope,  gas,  Bodlander,  40 
Bending  capillary  tubing,  114 
Benzene,  253 

absorption  of,  by  alcohol,  253 
absorption  of,  by  bromine  water, 

255 
absorption  of,  by  nickel  solution, 

255 

absorption  of,  by  paraffin  oil,  254 
determination  of,  253 
determination    of,    as    dinitro- 

benzene,  254 

determination  of,  in  coal  gas,  312 
separation    of,    from    ethylene, 

250,  259 


INDEX  OF  SUBJECTS 


423 


Benzoic  acid  for  calorimetry,  341 
Blast  furnace  gas,  306 

analysis  of,  330 

Blast  lamp  for  glass  blowing,  113 
Bleaching    powder,    evaluation    of, 

with  nitrometer,  401 
Bodlander  gas  baroscope,  40 
Bomb,  Mahler,  description  of,  331 

preparation  of,  337 
Boyle,  Law  of,  33 
British  thermal  unit,  346 
Bunte  gas  burette,  74 
Burette,  gas,  Bunte,  74. 

gas,  Hempel  simple,  51 

gas,  Honigmann,  72 

Hempel,  method  of  jacketing,  67 

modified  Winkler,  70 

with  correction  tube,  Hempel, 

9i 

Butylene,  separation  of,  from  ethy- 
lene,  250 


Calcium  carbide,  sampling  of,  356 
Calorimeter,  description  of,  335 

radiation  correction  for,  343 

water  equivalent  of,  340 

Junkers  gas,  347 

Junkers   gas,    manipulation   of, 

35i 

Junkers  gas,  preparation  of,  349 
Calorimeters,  331 
Candle,  sperm,  307 
Capillary    tube,    capacity    of,    per 

linear  centimeter,  62 
dimensions  of,  51,  53,  62 
method  of  bending,  114 
Carbon    bisulphide,    separation    of, 

from  carbon  oxysulphide,  279 
Carbon  dioxide,  225 

absorption    of,     by    potassium 
hydroxide,  225 


amount  of,  in  flue  gas,  295 

determination  of,  225 

determination  of,  in  atmospheric 
air,  by  Anderson  method,  387 

determination  of,  in  atmospheric 
air,  by  Hesse  method,  377 

determination  of,  in  atmospheric 
air,  by  Pettersson-Palmqvist 
method,  382 

determination  of,  in  coal  gas,  311 

determination  of,  in  flue  gas,  297 

determination  of,  in  sodium 
carbonate,  403 

recorder,  299 

relation  of,  to  oxygen  in  air,  377 
Carbon  monoxide,  226 

absorption  of,  231 

absorption  of,  by  cuprous  chlo- 
ride, 233 

colorimetric    determination    of, 

237 

detection  of,  226 

detection  of,  by  blood  spectrum, 
226 

detection  of,  in  blood,  227,  231 

detection  of,  with  iodine  pent- 
oxide,  231 

determination  of,  231 

determination  of,  by  fractional 
combustion,  239 

determination  of,  in  acetylene, 

369  ^ 

determination  of,  in  coal  gas,  313 

determination  of,  in  flue  gas,  298 

determination    of,    with    iodine 

pentoxide,  235 
Carbon  oxysulphide,  277 

absorbents  for,  278 

detection  of,  279 

determination  of,  279 

separation  of,  from  carbon  bi- 
sulphide, 279 


424 


INDEX  OF  SUBJECTS 


Carbon   oxysulphide,  separation  of, 

from  hydrogen  sulphide,  279 
Change  of  temperature,  error  caused 

by,  67 

Charles,  Law  of,  33 
Chlorine,  284 

determination  of,  285 
determination  of,  in  presence  of 

carbon  dioxide,  285 
determination  of,  in  presence  of 

hydrochloric  acid,  288 
Chloride  of  lime,  evaluation  of,  with 

nitrometer,  401 
Chromous    chloride,    absorption    of 

oxygen  by,  169 

Coal  briquet,  preparation  of,  333 
Coal,   example  of  determination  of 

heating  value  of,  345 
preparation  of  sample  of,  333 
Coal  gas,  306 

apparatus  for  analysis  of,  310 
complete  examination  of,  306 
constituents  of,  306 
determination      of     absorbable 

gases  in,  310 

determination  of  benzene  in,  312 
determination  of  carbon  dioxide 

in,  311 

determination  of  carbon  mon- 
oxide in,  313 
determination  of  cyanogen  in, 

263  ^ 

determination  of  heavy  hydro- 
carbons in,  312 
determination  of  naphthalene  in, 

318  ^ 

determination  of  nitrogen  in,  317 
determination  of  oxygen  in,  313 
determination  of  specific  gravity 

of,  309 

determination  of  total  sulphur 
in,  319 


Drehschmidt-Hempel      method 

for  sulphur  in,  320 
gas- volumetric  analysis  of,  309 
illuminating  power  of,  307 
Referees'  method  for  sulphur  in, 

320 
simultaneous    determination    of 

hydrogen  and  methane  in,  314 
simultaneous    determination   of 

methane  and  ethane  in,  314 
successive  determination  of  hy- 
drogen, methane  and  nitrogen 

in,  315 
volumetric     determination     of 

sulphur  in,  327 
Collection  of  gases,  i 

dissolved  in  liquids,  by  Hoppe- 

Seyler  method,  19 
dissolved  in  liquids,  by  Tiemann 

and  Preusse  method,  16 
Collection    of    gas    from    mercury 

pump,  13 
Collection    of    gases    from    mineral 

waters,  15 

from  reactions  in  sealed  tubes,  21 
from  springs,  15 
Combustible     substance,     standard, 

for  calorimeter,  341 
Combustion,  analysis  by,  147 

determination  of  gases  by,  141 
fractional,  of  hydrogen,  191 
fractional,    of    hydrogen,    with 

copper  oxide,  198 
fractional,    of    hydrogen,    with 

palladium-black,  196 
fractional,    of    hydrogen,    with 

platinum  or  palladium  asbes- 
tos, 192 

Combustion  of  gases,  127 
First  Case,  130 
Second  Case,  133 
Third  Case,  134 


INDEX  OF  SUBJECTS 


425 


Combustion  pipette,  Dennis,  147 
formation  of  oxides  of  nitrogen 

in,  152 

Combustion,  simultaneous,  of  hydro- 
gen, methane  and  carbon  mon- 
oxide, 244- 

with  Drehschmidt  tube,  154 
with  electrically  heated  spiral, 

147 
with   platinum   capillary   tube, 

154 
Confining  liquid,  running  down  of, 

68 

water,  saturation  of,  59 
Connection  of  apparatus,  113 
Connection    of    gas    pipette    with 

burette,  62,  64 
Connections,  rubber,  114 
Construction  of  apparatus,  113 
Copper,   absorption   of   oxygen  by, 

1 66 

Correction    tubes    for   Hempel   bu- 
rettes, 91 
Cuprous    chloride,    preparation    of 

acid  solution  of,  232 
preparation  of  ammoniacal  solu- 
tion of,  232,  233 
Cyanogen,  262 

amount  of,  in  illuminating  gas, 

265 

detection  of,  262 
detection  of,  in  presence  of  hy- 
drogen cyanide,  265 
determination  of,  263 
determination  of,  in  coal  gas,  263 
determination  of,  in  presence  of 
hydrogen  cyanide,  265 

D 

Dennis  combustion  pipette,  147 

manipulation  of,  149 
Dennis  spiral  absorption  pipette,  81 


Densities  of  gases,  theoretical,  406 
Determination  of  gases,  158 
Distillation  of  mercury,  119 
Double  absorption  pipette  for  solid 

and  liquid  reagents,  Hempel,  58 
Double  absorption  pipettes,  Hempel, 

56 

Drawing  off  of  gas  sample,  i 
Drehschmidt  tube,  combustion  with, 

154 


Efficiency  of  absorption  pipettes,  81 
Enamelled  rubber  tubing,  1 14 
Error  due  to  change  of  temperature 

during  analysis,  67 
Ethane  and  methane,  possible  errors 

in  combustion  of,  131 
simultaneous  determination  of, 

in  coal  gas,  314 
Ethylene,  248 

absorption  of,  by  bromine,  249 
absorption   of,   by   fuming   sul- 
phuric acid,  249 
determination  of,  249 
determination  of,  in  presence  of 

acetylene,  249 
separation  of,  from  benzene,  250, 

259- 

separation  of,  from  butylene,  250 
Exact  analysis  over  mercury,  Hempel 

apparatus  for,  90 
Exact  apparatus  without  stopcocks, 

Hempel,  99 
Explosion,  analysis  by,  141 

analysis,  proportion  of  gases  in, 

143 

pipette  for  exact  analysis,  146 
pipette    for    technical   analysis, 

141 

Extraction  of  gases  from  minerals, 
21 


426 


INDEX  OF  SUBJECTS 


Ferrous  salts,  absorption  of  oxygen 

by,  1 68 
Filling  of  gas  pipettes  with  liquid 

reagents,  57 

Fittings  of  the  laboratory,  49 
Flue  gas,  amount  of  carbon  dioxide 

in,  295 

Flue  gas,  analysis  of,  295,  297 
automatic  analysis  of,  299 
average  sample  of,  296 
sampling  of,  2 
Fluorine,  determination  of,  280 

determination  of,  in  presence  of 

carbon  dioxide,  280 
determination  of,  in  teeth,  284 
Formation  of  oxides  of  nitrogen  in 

combustion  pipette,  152 
in  explosion  analysis,  144 
Fractional  combustion  of  hydrogen, 

191 

with  copper  oxide,  198 
with  palladium-black,  196 
with     platinum     or    palladium 

asbestos,  192 
Friedrichs  spiral  gas  washing  bottle, 

123,  124 
Fuel  gas,  306 

Fuels,  liquid  and  gaseous,  determina- 
tion of  heating  value  of,  347 
solid,  determination  of  heating 

value  of,  331 

Fuming   sulphuric   acid,   absorption 
of  heavy  hydrocarbons  by,  247 
pipette  for,  247 
Furnace  gases,  sampling  of,  i 


Gas  baroscope,  Bodlander,  40 
Gas  calorimeter,  automatic,  354 

Junkers,  347 

Junkers,  manipulation  of,  351 


Junkers,  preparation  of,  349 
Gas,  determination  of  specific  gravity 

of,  44 

Gaseous  fuels,  determination  of  heat- 
ing value  of,  347 

hydrocarbons  and  nitrogen,  de- 
termination by  combustion, 
136 

hydrocarbons,  identification  of, 

'  by  combustion,  138 
Gases,  combustion  of,  127 

determinable  by  combustion, 
127,  128 

determination  of,  158 

determination  of,  by  combus- 
tion, 141 

dissolved  in  liquids,  collection  of, 
by  Hoppe-Seyler  method,  19 

dissolved  in  liquids,  collection 
of,  by  Tiemann  and  Preusse 
method,  16 

from  mineral  waters,  collection 
of,  15 

from  reactions  in  sealed  tubes, 
collection  of,  21 

from  springs,  collection  of,  15 

measurement  of,  33 

properties  of,  158 

proportion  of,  in  analysis  by  ex- 
plosion, 143 

readily  soluble,  determination 
of,  70 

variations     in     gram-molecular 

volumes  of,  139 

Gas  from  mercury  pump,  collection 
of,  13 

generator,  oxyhydrogen,  145 

measurement  of  large  samples 
of,  28 

meter,  28 

methods  for  determining  quan- 
tity of,  33 


INDEX  OF  SUBJECTS 


427 


Gasometers,  23 
Gas  refractometer,  304 
Gas  volume,  reduction  of,  to  stand- 
ard conditions,  33 

tables  for  reduction  of,  407 
Gas  volumeter,  Lunge,  37 

Lunge,  objections  to,  39 
Gas  volumetric  analysis  of  coal  gas, 

309 
Gas    washing     bottle,    spiral,    123, 

124 

Generator,  oxyhydrogen,  145 
Glass  blowing,  113 

blast  lamp  for,  113 
glass  tubing  for,  113 
Gram-molecular  volumes,  variations 

in,  139 

Gross  heating  value,  352,  354 
Gun  cotton,  analysis  of,  393 

H 

Hankus  absorption  pipette,  79 
Heating  value  of  coal,  example  of 

determination  of,  345 
of  fuel,  combustion  of  sample, 

339 

of  fuel,  determination  of,  331 
of  gaseous  fuels,  total,  gross  and 

net,  352,  354 

of  liquid  and  gaseous  fuels,  de- 
termination of,  347 
Heavy  hydrocarbons,  246 
absorption  of,  246 
determination  of,  in  coal  gas,  312 
Hefner  lamp,  307 
Heinz  absorption  pipette,  80 
Helium,  213 
Hempel     apparatus,     accuracy     of 

analyses  with,  67 
for  exact  analysis  over  mercury, 

90 
portable,  69 


Hempel    burettes    with    correction 

tubes,  91 
Hempel   double   absorption   pipette 

for  liquid  reagents,  56 
for  solid  and  liquid  reagents,  58 
Hempel    exact    apparatus    without 

stopcocks,  99 
Hempel    gas    burette,    method    of 

jacketing,  67 
Hempel  pipette,  absorption  of  a  gas 

with,  6 1 
Hempel  simple  absorption  pipettes, 

53 

Hempel  simple  gas  burette,  51 
Hesse  method,  collection  of  samples 
of  air,  379 

for  carbon  dioxide  in  air,  377 

solutions  used  in,  378 
Honigmann  gas  burette,  72 
Hydrocarbons,  classes  of,  determin- 
able  by  combustion,  127 

gaseous,    and    nitrogen,    deter- 
mination by  combustion,  136 

gaseous,    identification    of,    by 
combustion,  138 

heavy,  246 

heavy,  absorption  of,  246 
Hydrogen.  181 

absorption    of,    by    palladium- 
black,  188 

and  methane,  simultaneous  de- 
termination of,  in  coal  gas,  314 

detection  of,  181,  182 

determination  of,  by  absorption, 
182 

determination  of,  by  explosion, 
186 

determination  of,  in  presence  of 
methane,  242 

determination  of,  with  combus- 
tion pipette,  187 

fractional  combustion  of,  191 


428 


INDEX  OF  SUBJECTS 


Hydrogen,  fractional  combustion  of, 
with  copper  oxide,  198 

fractional  combustion  of,  with 
palladium-black,  196 

fractional  combustion  of,  with 
platinum  or  palladium  asbes- 
tos, 192 

in  acetylene,  determination  of, 
356 

methane  and  nitrogen,  successive 
determination  of,  in  coal  gas, 

3i5 
Hydrogen  chloride,  289 

determination  of,  289 
Hydrogen  cyanide,  269 
detection  of,  269 
detection    of,    in    presence    of 

cyanogen,  267 
determination  of,  269 
determination  of,  in  presence  of 

cyanogen,  267 

Hydrogen  dioxide,   detection  of,   in 
presence  of  ozone  and  nitrogen 
tetroxide,  171,  175 
evaluation  of,  with  nitrometer, 

401 
reagents  for  detection  of,   171, 

172 
Hydrogen   peroxide    (see  Hydrogen 

dioxide) 
Hydrogen  pipette,  144 

for  exact  analysis,  147 
Hydrogen  sulphide,  270 
detection  of,  271 
determination  of,  272 
separation  of,  from  carbon  oxy- 

sulphide,  279 
Hygrodeik,  375 

Humidity,  absolute  and  relative,  371 
of   the   atmosphere,   determina- 
tion of,  371 
relative,  calculation  of,  374 


Identification  of  gaseous  hydrocar- 
bons by  combustion,  138 
Ignition  wire,  337 
Illuminating  gas,  306 

amount  of  cyanogen  in,  265 

analysis  of,  306 

determination   of   cyanogen  in, 

328 
determination  of  heating  value 

of,  347 
determination    of    illuminating 

power  of,  307 
determination  of  naphthalene  in, 

3i8 
determination  of  specific  gravity 

of,  309 
determination  of  total  sulphur 

in,  319 

volumetric  analysis  of,  309 
Illuminating  power,  computation  of, 

308 

of  coal  gas,  determination  of,  307 
Impurities  in  commercial  acetylene, 

355 

Induction  coil,  144 
International  atomic  weights,  405 
Iodine  pentoxide,  detection  of  carbon 

monoxide  with,  231 
determination   of   carbon   mon- 
oxide with,  235 
Iron  ignition  wire,  337 


Jacketing  of  Hempel  gas  burette,  67 
Junkers  automatic  gas  calorimeter, 

354 

gas  calorimeter,  347 
gas    calorimeter,    manipulation 

of,  35i 
gas  calorimeter,  preparation  of, 

349 


INDEX  OF  SUBJECTS 


429 


Krypton,  213 


Laboratory,  arrangement  of,  49 

Large  samples  of  gas,  measurement 
of,  28 

Laws     concerning     combustion     of 
gases,  127 

Law  of  Boyle,  33 

Law  of  Charles,  33 

Liquid  fuels,  determination  of  heat- 
ing value  of,  347 

Liter  weights  of  gases,  406 

Lubricant  for  stopcocks,  preparation 
of,  115 

Lubrication  of  stopcocks,  115 

Lunge  gas  volumeter,  37 
nitrometer,  397 
ureometer,  397 

M 

Mahler  bomb,  description  of,  331 
Marsh  gas  (see  Methane) 
Measurement  of  gases,  33 

of    large    samples    of    gas,    by 

bottle  and  cylinder,  28 
of  large  samples  of  gas,  by  gas 

meter,  28 

of  large  samples  of  gas,  by  rota- 
meter,  32 
Mercury,  distillation  of,  119 

impurities  in  commercial,  117 

purification  of,  117 

pump,  8 

pump,   collection   of  gas  from, 

13 

pump,  description  of,  9 
pump,  method  of  working,  12 
Metaphosphoric    acid    as    lubricant 
for  stopcocks,  116 


Methane,  240 

and  ethane,  possible  errors  in 
combustion  of,  131 

and  ethane,  simultaneous  deter- 
mination of ,  131,  203 

and  ethane,  simultaneous  de- 
termination of,  in  coal  gas, 
3i4 

and  hydrogen,  simultaneous  de- 
termination of,  in  coal  gas, 

3H 

combustion  of,  in  Dennis  pipette, 
246 

determination  of,  241 

determination  of,  by  combus- 
tion, 241 

determination  of,  in  presence  of 
hydrogen,  242 

hydrogen  and  nitrogen,  succes- 
sive determination  of,  in  coal 
gas,  315 

in  acetylene,  determination  of, 

369 

Minerals,  extraction  of  gases  from,  21 
Mineral  waters,  collection  of  gases 

from,  15 

Modified  Winkler  gas  burette,  70 
Moisture  in  the  atmosphere,  deter- 
mination of,  371 
Mounting  of  apparatus,  114 

N 

Naphthalene,  260 

determination  of,  260 

determination  of,  in  coal  gas,  318 

for  calorimeter,  342 
Natural  gas,  306 
Neon,  213 

Net  heating  value,  352,  354 
Nickel  cyanide,  ammonia,  prepara- 
tion of  solution  of,  256 
Nitric  acid  esters,  analysis  of,  393 


43° 


INDEX  OF  SUBJECTS 


Nitric  oxide,  217 

absorption  of,  219 
combustion  of,  219 
detection  of,  218 
determination  of,  219 
volumetric     determination     of, 

220 

Nitrites  in  the  atmosphere,  deter- 
mination of,  222 
Nitrogen,  206 

absorption  of,  207 
and  gaseous  hydrocarbons,  de- 
termination   by    combustion, 
136 

and  oxygen  in  acetylene,  deter- 
mination of,  369 
determination   of,   in  coal  gas, 

3i7 
determination   of,   in  gas   mix^ 

tures,  317 
oxides,  formation  of,  in  explosion 

analysis,  144 
separation  of,  from  argon  group, 

209,  212 
Nitrogen    peroxide     (see    Nitrogen 

tetroxide) 
Nitrogen  tetroxide,  223 

detection  of,  in  presence  of  ozone 
and    hydrogen    dioxide,    171, 

175 
reagents  for  detection  of,  171, 

172 

Nitrometer,  393 
Lunge,  397 

Nitroglycerine,  analysis  of,  393 
Nitrous  acid,  determination  of  sul- 
phur dioxide  in  presence  of,  276 
Nitrous  oxide,  213 

combustion  of,  214 
detection  of,  213 
determination  of,  214 
Nowicki  absorption  pipette,  80 


Orsat  apparatus,  78 

objections  to  usual  form  of,  79, 

84,85 
Orsat-Dennis  apparatus,  85 

accuracy  of,  89 

Oxides  of  nitrogen,  formation  of,  in 
combustion  pipette,  152 

formation  of,  in  explosion  analy- 
sis, 144 

reduction  by  mercury,  393 
Oxygen,  158 

and  nitrogen  in  acetylene,  de- 
termination of,  369 

determination  of,  158 

determination  of,  by  absorption, 
1 60 

determination  of,  by  combus- 
tion, 159 

determination  of,  in  coal  gas,  313 

determination  of,  in  flue  gas,  298 

determination  of,  in  presence  of 
acetylene,  253 

determination  of,  in  presence  of 
hydrogen  sulphide  and  carbon 
dioxide,  169 

determination  of,  with  alkaline 
pyrogallol,  160 

determination  of,  with  copper 
eudiometer,  159 

removal  of,  from  air,  229 
Oxyhydrogen  gas  generator,  145 

removal  of  ozone  in,  146 
Ozone,  170 

detection  of,  170 

detection  of,  in  presence  of  nitro- 
gen tetroxide  and  hydrogen 
dioxide,  171,  174 

determination  of,  179 

formation  of,  in  hydrogen  flame, 
175 


INDEX  OF  SUBJECTS 


431 


Ozone,  in  atmospheric  air,  detection 

of,  178 
production    of,     by    action    of 

sulphuric   acid   upon   barium 

dioxide,  177 
production  of,  by  silent  electric 

discharge,  176 
production  of,  by  slow  oxidation 

of  phosphorus,  178 
reagents  for  detection  of,   171, 

172 
removal  of,  in  oxyhydrogen  gas, 

146 


Palladium  asbestos,  preparation  of, 

iQ5 

Palladium-black,   absorption  of  hy- 
drogen by,  1 88 
preparation  of,  196 
regeneration  of,  189 
Palladium,  colloidal,  preparation  of, 

182 

solution  for  absorption  of  hydro- 
gen, 183 
tube,  determination  of  volume  of 

oxygen  in,  189 
Pentane  lamp,  307 
Pettersson-Palmqvist     method     for 

carbon  dioxide  in  air,  382 
Phosphine,  290 

absorption  of,  by  sodium  hypo- 

chlorite,  362 
amount  of,  in  crude  acetylene, 

357 

detection  of,  291 
determination  of,  291 
determination  of,  in  presence  of 

acetylene,  291 
in  acetylene,  determination  of, 

357 


Phosphorus,  gas  pipette  for,  56 

in  solution,  absorption  of  oxygen 

by,  1 66 

Phosphorus  pentoxide,  as  dehydrat- 
ing agent,  n 
impurities  in,  n 
Phosphorus,     preparation     of     thin 

sticks  of,  164 
solid,  absorption  of  oxygen  by, 

163 

Photometric  units,  307 
Photometer,  Bunsen,  308 
Photometry,  307 

Picric  acid,  determination  of  naph- 
thalene with,  260 
Pintsch  gas,  306 
analysis  of,  329 
composition  of,  329 
Pipette,  absorption,  double,  Hempel, 

56 
absorption,  for  liquid  reagents, 

simple,  Hempel,  53 
absorption,  for  solid  and  liquid 

reagents,  simple,  Hempel,  55 
absorption,  Hankus,  79 
absorption,  Heinz,  80 
absorption,  mercury,  96 
absorption,  Nowicki,  80 
combustion,  Dennis,  147 
combustion,  Dennis,  manipula- 
tion of,  149 
combustion,  formation  of  oxides 

of  nitrogen  in,  152 
explosion,    for    exact    analysis, 

146 
explosion,  for  technical  analysis, 

141 
for  phosphorus,  of  brown  glass, 

165 
for   solid   and   liquid   reagents, 

double,  Hempel,  58 
gas,  for  phosphorus,  56 


432 


INDEX  OF  SUBJECTS 


Pipette,  gas,  method  of  fastening  to 

stand,  54 
Hempel,    absorption   of   a    gas 

with,  6 1 
hydrogen,  144 
hydrogen,    for    exact    analysis, 

147 

spiral  absorption,  Dennis,  81 
stand  for,  54 

Platinum    capillary    tube,    combus- 
tion with,  154 

Portable  Hempel  apparatus,  69 
Potassium    hydroxide,    strength    of 

solution  of,  225 

Potassium  permanganate,  standard- 
ization of,  with  nitrometer,  400 
Press  for  coal  briquet,  334 
Producer  gas,  306 

analysis  of,  330 

Properties  of  various  gases,  158 
Proportion  of  gases  in  analysis  by 

explosion,  143 
Propylene,  250 
Psychrometer,  August,  375 
whirling,  372 

whirling,  manipulation  of,  373 
Pump,  mercury,  8 

mercury,  method  of  working,  12 
Purification  of  mercury,  117 

by  concentrated  sulphuric  acid 
and  mercurous  sulphate,  117, 
119 

by  distillation,  117,  119 
by  nitric  acid,  118 
Pyrogallol,  alkaline,  preparation  of, 

1 60 

Pyrolusite,   evaluation   of,   with  ni- 
trometer, 402 


Quantity  of  a  gas,  methods  for  de- 
termining, 33 


Radiation  correction,  343 
Reagents,  analytical  absorbing  power 

of,  65 

Recorder  of  carbon  dioxide,  299 
Reduction  of  gas  volumes,  33 

of  gas  volume,  tables  for,  407 
"Referees'  Test,"  for  total  sulphur, 

3i9 

Refractometer,  gas,  304 
Relative  humidity,  371 

calculation  of,  374 
Rotameter,  32 
Rubber  bulb  aspirator,  7 

connections,  114 

tubing,  enamelled,  114 

tubing,  objections  to,  for  con- 
nections, 2 
Running  down  of  confining  liquid,  68 


Saltpeter,  analysis  of,  393 

Sample,  drawing  off  of,  i 

Samples    of    gas,    measurement    of 
large,  28 

Sampling  of  air,  3 
of  flue  gas,  2 
of  furnace  gases,  i 
of  gas  from  gas  mains,  2 
tube  for  furnace  gases,  i 
tube   for   furnace  gases,  Wink- 

ler,  i 

tube  for  gas  from  mains,  3 
tube,  Huntly,  5 
tubes  for  air,  3 
tubes,  glass,  with  stopcocks,  4 

Saturation  of  confining  water,  59 

Sealed  tubes,  collection  of  gases  from 
reactions  in,  21 

Silicon  hydride  in  acetylene,  deter- 
mination of,  368 


INDEX  OF   SUBJECTS 


433 


Silicon  tetrafluoride,  290 
Silver  solution,  ammoniacal,  prepara- 
tion of,  249 
Simple  absorption  pipette  for  liquid 

reagents,  Hempel,  53 
for   solid    and    liquid    reagents, 

Hempel,  55 
Sodium  carbonate,  analysis  of,  with 
nitrometer,  403 

hypochlorite,       absorption      of 

phosphine  by,  362 
hyposulphite,      absorption      of 

oxygen  by,  168 
hyposulphite,  reaction  of,  with 

oxygen,  168 
Solid     phosphorus,     absorption     of 

oxygen  by,  163 

Soluble  gases,  determination  of  read- 
ily, 70 

Specific  gravity  of  coal  gas,  determin- 
ation of,  309 

Specific  gravity  of  a  gas,  determina- 
tion of,  by  method  of  Bunsen,  44 
by  method  of  Pannertz,  44 
by  method  of  Schilling,  44 
Spectrum  of  blood,  227 

of  carbon  monoxide  hsemoglobin, 

227 

Sperm  candle,  307 
Spiral  absorption  pipette,  81 

gas  washing  bottle,  123,  124 
Springs,    collection    of    gases    from, 

IS 
Standard  combustible  substances  for 

calorimeter,  341 
Stands  for  gas  pipettes,  54 
Stibine,  293 
Stopcocks,  115 

lubrication  of,  115 
Storage  of  gases,  i 
Sucrose  for  calorimeter,  341 


Suction  pump  and  rubber  bulb  aspi- 
rator, 8 

brass,  8 

water,  8 

Sulphur,  determination  of,  in  acety- 
lene, 367 

determination  of,  in  coal  gas,  319 

in  acetylene,  source  of,  367 

in  coal  gas,  Drehschmidt-Hempel 
method  for,  320 

in  coal  gas,  Referees'  method  for, 
320 

in  coal  gas,  volumetric  method 

for,  327 
Sulphur  dioxide,  273 

determination  of,  274 

determination  of,  in  flue  gas,  299 

determination  of,  in  presence  of 

nitrous  acid,  276 

Sulphuric  acid,   fuming,   absorption 
of  heavy  hydrocarbons  by,  247 

fuming,  pipette  for,  247 


Ten-bulb  tube,  Lunge,  359 

Tension  of  aqueous  vapor,  table  of, 

411 

Theoretical  densities  of  gasesj  406 
Topler  pump,  collection  of  gas  from, 

13 

description  of,  9 
method  of  working,  12 
Total  heating  value,  352 
Tubes,  sampling,  for  furnace  gases,  i 

sampling,  of  glass,  3,  &  5 
Tubing,  capillary,  method  of  bending, 

114 
rubber,  enamelled,  114 

U 
Ureometer,  Lunge,  397 


434 


INDEX  OF  SUBJECTS 


Vapor,  tension  of  aqueous,  411 
Ventilation,  effects  of  poor,  376 
Volumeter,  gas,  Lunge,  37 

W 

Water  equivalent  of  calorimeter,  340 
example  of  determination  of,  342 

Water  gas,  306 

suction  pump,  8 

Weight    of    gas,    determination    of, 
from  its  pressure,  40 


Weights  of  one  liter  of  different  gases, 
406 

Wet  and  dry  bulb  thermometers,  371 

Whirling  psychrometer,  372 
manipulation  of,  373 

Winkler  absorption  apparatus,  124 

Winkler-Dennis  absorption   appara- 
tus, 125 

W'inkler  gas  burette,  70 


X 


Xenon,  213 


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our  chemical  industries,  as  well  as  the  protection  of  the  consumer,  de- 
mands all  the  aid  which  a  skillful  application  of  these  methods  is  able 
to  bring.  Professor  Sherman's  book  contains  the  well-ordered  mate- 
rial for  such  a  course  of  instruction.  —  Technology  Quarterly. 

A  feature  of  the  book  that  commends  itself,  is  the  general  presenta- 
tion of  a  subject  in  one  chapter,  that  on  carbohydrate  for  example, 
followed  by  a  chapter  upon  the  special  methods  of  analysis.  When 
it  is  impracticable  to  give  all  the  methods  for  the  analysis  of  the 
various  compounds  considered,  references  are  made  to  standard 
works  upon  the  subject;  these  are  often  supplemented  by  copious 
foot-notes  making  the  book  encyclopedic  in  scope. 

—  Journal  of  the  American  Chemical  Society. 

Commendable  features  are:  the  free  use  of  references  in  the  form 
of  both  foot-notes  and  bibliographical  compilations;  the  carefully 
worked  out  procedures;  the  clear  and  pertinent  notes  and  discussions. 
The  isolated  student  or  casual  worker  in  methods  of  organic  analysis 
will  find  the  book  of  especial  value  in  pointing  out  original  and  often 
scattered  sources  of  information.  —  Science. 

While  this  book  is  not  primarily  intended  for  medical  students  or 
physicians,  it  presents  a  concise  yet  complete  treatment  of  the  subject 
of  organic  analysis  including  the  analysis  of  food  products  such  as 
milk,  cereals,  butter,  etc.  It  will  be  especially  useful  to  students  in 
advanced  courses  or  in  post-graduate  work  who  are  fitting  themselves 
for  the  position  of  food  experts  or  as  agricultural  chemists. 

—  Medical  Record. 


THE  MACMILLAN  COMPANY 

Publishers          64-66  Fifth  Avenue          New  York 


A  College  Text-Book  on  Quantitative  Analysis 

BY  HERBERT  RAYMOND  MOODY,  PH.D. 

Associate  Professor  of  Analytical  and  Applied   Chemistry  in  the 
College  of  the  City  of  New  York 

Cloth,  8vo,  165  pages,  $1.25  net 

With  the  ordinary  manual  the  student  is  inclined  to  proceed 
blindly  without  understanding  the  facts  of  the  process  or  the 
chemical  changes  which  are  taking  place.  Before  every  analysis, 
therefore,  Professor  Moody  has  outlined  each  consecutive  step 
and  given  a  resume  of  every  reaction  which  should  take  place 
as  well  as  those  which  may  occur  in  case  the  student  makes  an 
error  or  fails  to  follow  the  directions.  He  has  also  included 
sample  calculations  wherever  the  student  really  needs  such 
assistance. 

Only  such  facts  and  theories  as  are  necessary  to  the  full  under- 
standing of  the  development  of  the  subject  have  been  included. 
There  is  much  possible  latitude  in  the  choice  of  detail  of  methods 
in  the  analyses  selected,  but  only  standard  methods  which  have 
been  found,  after  years  of  experience,  to  serve  satisfactorily, 
have  been  chosen.  Not  only  in  this  selection  but  in  all  other 
practical  details,  the  author  has  been  greatly  assisted  by  the 
use  of  the  book  in  preliminary  form  with  large  numbers  of  stu- 
dents during  the  last  five  years. 

CONTENTS 

Section     I.    GRAVIMETRIC  ANALYSIS 3 

Section   II.     ELECTROLYTIC  ANALYSIS 83 

Section  III.    VOLUMETRIC  ANALYSIS 95 

INTERNATIONAL  ATOMIC  WEIGHTS 156 

LOGARITHMS 157 


PUBLISHED  BY 

THE  MACMILLAN  COMPANY 

Publishers          64-66  Fifth  Avenue          New  York 


A  Course  in  Qualitative  Chemical  Analysis 

BY  CHARLES  BASKERVILLE,  PH.D.,  F.  C.  S. 

Professor  in  the  Department  of  Chemistry, 

College  of  the  City  of  New  York 

AND 

LOUIS  J.  CURTMAN,  PH.D. 

Instructor  in  the  Department  of  Chemistry, 
College  of  the  City  of  New  York 

Cloth,  8vo,  200  pages,  $1.40  net 

.  The  essential  features  of  this  book  may  be  seen  from  the  plan  which 
is  here  briefly  outlined. 

1.  The  chief  reactions  of  the  metals  are  first  given  with  sufficient 
detail  and  completeness  to  enable  the  student  to  thoroughly  under- 
stand the  basis  of  and  the  limitations  to  the  schemes  of  analysis 
adopted.     Reactions  not  utilized  in  the  schemes  are  also  given  to 
supply  information  which  may  be  turned  to  account  in  making  addi- 
tional confirmatory  tests  and  in  devising  schemes  other  than  those 
given;  they  also  supply  a  number  of  qualitative  facts  upon  which 
important  quantitative  methods  are  based.    As  the  vast  majority  of 
students  who  take  Qualitative  Analysis  subsequently  pursue  a  course 
in  Quantitative  Analysis,  this  information  supplies  the  foundation,  of 
fact  which  we  believe  should  be  given  in  the  qualitative  course. 

2.  An  outline  of  the  method  of  analysis  to  be  employed  follows.    This 
is  in  the  nature  of  a  resume  of  the  chief  reactions,  in  which  distinctions 
are  emphasized  with  a  view  to  their  use  in  separations.    Details  in 
manipulation  are  purposely  omitted  in  this  discussion,  in  order  that 
the  main  features  and  chemistry  thereof  may  be  clearly  understood. 

3.  The  scheme  of  analysis  is  then  taken  up.    The  directions  are 
clear,  especial  attention  being  given  to  the  amounts  of  reagents  to  be 
taken,  as  well  as  the  most  appropriate  vessel  to  be  used  and  its  size. 

4.  Then  follow  notes.     Under  this  head,  additional  information, 
which  would  obstruct  the  reading  of  the  text,  is  supplied.     This 
information  is  intended  to  supply  the  reasons  for  unusual  details  or 
procedures  in  the  text  and  precautions  that  are  to  be  taken,  but  it 
applies  chiefly  to  matters  relating  to  the  correcting  of  errors  and  to 
the  clearing  up  of  doubtful  results.    Supplying  the  reasons  for  every 
step,  it  is  believed,  will  go  a  long  way  toward  doing  away  with  the  too 
frequent  practice  of  blindly  following  directions. 


PUBLISHED  BY 

THE  MACMILLAN  COMPANY 

Publishers          64-66  Fifth  Avenue  New  York 


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